A strong trough digging ESE out of the Rockies with an associated ULJ will promulgate a disturbance across the Central Plains this evening into the Middle Mississippi River Valley and off into the Ohio River Valley towards the mid-Atlantic region by Friday morning.  A broad swath of heavier snowfall amounts from 4″ – 6″ is likely across the I-70 corridor from Kansas City, MO to near St. Louis, MO, with locally higher amounts of 7″ – 8″ possible in areas that experience the best frontogenetic forcing within the most favorable UVV/Omega zone.

Across the I-70 corridor overnight forecast QPF (total precipitation) values of 0.35″ – 0.43″ juxtaposed with the most favorable dendritic growth zone (ice crystal growth rate as a function of temperature) on the order of 100 mb (mean) and mean SLER (snow to liquid equivalent ratio) of 15:1.  As the system moves off into the mid-Atlantic region by FRI, snowfall amounts of 6″ to 12″ are not out of the question.

ChaserTV will have some live streams available for this event, so stay tuned to our live streams to watch the event as it unfolds across the region.

JLR

View 01/19 – 01/20/11 in a larger map

Current Surface Map per HPC

Forecast low pressure track ensembles through FRI

24 hr probability of snowfall 2"+ per HPC

SREP mean precip. / UVV/ Omega

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SYNOPSIS

Two major winter systems are taking shape over the continental United States, with the biggest weather maker being the gulf low that is currently sitting over far SE TX.  This low is forecast to move proximal to the Gulf Coast as it treks from near Corpus Christi, TX (1002 mb) this morning to near Jacksonville, FL by Monday evening, weakening slightly to near 1014 mb before moving into the Atlantic and strengthening (again) as it takes aim on the eastern seaboard.  The HPCs low track ensemble blend appears below (FIG 1).

This system will have ample gulf moisture to work with, with a warm layer aloft, along with ample cold air advection at the surface, meaning a wide variety of winter precipitation is in store for parts of the Gulf-Atlantic coastal plain region.  As you can see, freezing temperatures (FIG 2) currently extend all the way from NE TX to south of Atlanta, GA as a wedge of cold air interacts with ample warm, moister air sitting proximal to the Gulf of Mexico.

While snowfall amounts of 3-6+ inches will be possible across a broad section of the south, a wedge of warm air aloft will introduce the potential for ice as well, especially along and south of the I-20 corridor.  Though there is some dubiety as to where the actual rain/freezing rain/sleet and snow lines will fall, as winter systems are often difficult to forecast in this regard, this sounding below from near Montgomery, AL for tonight clearly shows the warm layer aloft atop surface temps just below the 0C (32 degrees F) freezing mark (see FIG 3 SKEW-T).

The system looks to be quite the prolific weather maker as it gyrates along the Gulf Coast and makes its way off into the Atlantic region overnight on Monday.  The HPC’s forecast snow (FIG 4) and ice accumulation (FIG 5) maps appear below, along with the SREF ensembles winter precipitation forecasts for the southern system (FIG 6).

Additionally, a longer duration snow event is on tap for parts of the Midwest, as a disturbance moves across that region, possibly dumping heaving snowfalls of 4″ – 8″ across a wide swath from NE into parts of MO and possibly SW IL through early Tuesday (see tomorrow’s FIG 7 HPC snowfall probabilistic graphic below for the Midwest).

As your go-to source for live and breaking severe weather video feeds, please tune back in to ChaserTV throughout the next 48 hours as we offer some streamer feeds from one or both of these regions as these potentially hazardous winter weather events unfold.  Folks across parts of the SE who will be impacted by the most adverse weather, including ice, should prepare for this event accordingly, staying tuned to local weather bulletins and preparing for the impossibility of travel, along with the potential for extended power outages where heavier ice accumulations are found.

JLR

Note: click on any of these images for a larger view.

FIG 1

FIG 2 - Current 2m Temps

FIG 3 - NAM Forecast SKEW-T

FIG 4 - Probability of snowfall >/= 4 inches through 7 AM MON

FIG 5 -Probability of ice accumulations >/= 0.25 inch through 7 AM MON

FIG 6- Preciptation Types (likely) per NCEP at 12z MON (Green - rain / Blue - snow / Red - freezing rain / Orange - sleet)

FIG 7 - MON Probabilistic Snowfall

A strong trough will dig equatorward, reaching into the Southern Plains by Friday. An associated surface cyclone will gravitate poleward from the northern TX panhandle (0z Friday) to southeast Minnesota (0z Saturday), deepening as it arrives in the western Great Lakes region early Saturday. Ample cold air and QPF on the back side of the system will support heavy snowfall of 6” -12” (see white shaded area on the map below) in parts of the Central and Northern Plains.

However, extremely strong shear will be found to the right of the mid-level jet core as it rounds the basal side of the trough, with SFC-500 mb bulk shear profiles of 50-70 kts present across a broad section of the western Gulf Coast extending northward into the Lower and Mid-Mississippi Valley region. As typical with winter setups, there will be fairly high amounts of shear overlapping what will probably be mostly meager MLCAPE values of 250 – 750 J/KG, though some higher values (AOA 1000 J/KG) may be found over parts of E TX into LA. The plenteous shear profiles will be courtesy of a strong SW – NE Upper Level jet core of 130+ kts juxtaposed with a mid-level jet core of 110+ kts and a strong WSW LLJ jet of 40-50 kts across the region. With such strong forcing and deep layer flow/shear vectors forecast, per rawinsonde data, to be parallel to the attendant cold front, a more linear mode of convection appears probable in the greatest risk area (see red shaded area on the map below).

Upper-level divergence proximal to the main jet core should help to erode CINH by FRI afternoon, allowing for semi-steep lapse rates. In this warm sector, 0-30m Td values are progged to reach 55-60 (F) across much of the Lower and Middle Mississippi Valley, though instability concerns remain due to the models showing some ongoing precipitation across the best severe risk area early in the period. The extent of any instability that is able to materialize will be highly dependent upon what, if any, clearing is able to take place. However, given the strong forcing and shear profiles across the region, it won’t take much to produce at least a line on SVR t-storms capable of damaging winds and some hail, though an attendant TOR risk can’t be ruled out, either.

Since we’re still 36-48 hours away from the event, none of the mesoscale details will be refined until closer to the event. Also, it should be noted that some synoptic-scale details also remain in question, such as the exact track and strength of the surface cyclone, as well as the actual amount of QPF on the NW side of the cyclone, which will influence snowfall amounts across the Northern Plains.
Stay tuned to ChaserTV, as we’ll likely have live streaming from one or both parts of this system as adverse weather evolves on Friday.

Forecast written for ChaserTV by Convective Addiction’s Jesse Risley.

View New Year’s Eve Storm in a larger map

18z Surface map (GFS) - 20101231

MLCAPE - 18z 20101231

H5 profile - 18z 20101231

2m Theta-E 18z 20101231

The good news is that many areas will still likely see a white Christmas; while holiday travels in some areas will be molested by the onset of this system, the bad news is that winter storm aficionados will not likely be seeing a major 12+ inch snowfall event across parts of the country’s midsection.  I would expect further model changes with the final 12z suite of model outputs, but some basic forecast thoughts can be shared for our readers.

A split flow pattern will persist across the CONUS, with essentially two branches of energy: a northern and a southern stream.  The dome of cold air entrenched across the northern CONUS, coupled with the an emerging impulse across the northern plains, will be the major snowfall impetus for the immediate period.  Forecast QPF (precipitation amounts) with this impulse, as it produces plenteous forcing, appear to range from 0.10″ to 0.30″ (some aberrations in those amounts appear likely), which when coupled with ambient surface and tropospheric temperature profiles, appears to equate to a broad area of 2″ – 5″ snowfall totals (using a 15:1 average snowfall to liquid ratio).  In areas that see the maximum lift from this system, totals exceeding 5″ – 6″ are not at all implausible.  Some of the SKEW-Ts across the Ozarks region indicate a shallow layer of warm air aloft (i.e., 750 mb – 850 mb) juxtaposed with surface temperatures at the 0C (freezing) mark, so some minor icing is possible in those areas as the southern impulse moves northeastward.

The southern stream of this split flow pattern will begin gyrating out of the Southern Plains into the Gulf-Atlantic Coastal Plains region, and it will have the most bounteous moisture to work with, henceforth pilfering the better moisture from being engrossed by the northern branch as it peregrinates southeastward towards the Blue Ridge/Tennessee Valley regions.  There should be some phasing of both the northern and the southern stream heading into Christmas Day, which could spell trouble for the north-central Appalachian region, precipitation wise, and the evolution of that event should be better refined by both the rest of today’s 12z and Friday’s 00z model runs.

I’ve included a map below with some preliminary winter precipitation forecast types/amounts for FRI – early SAT, with the area highlighted in orange being that which is most likely to see snowfall amounts ranging between 2″ – 5″ (locally higher totals possible), whereas the light pink areas of the Ozarks correlating with favorable (forecast) atmospheric conditions for some light icing.

Please have a safe and joyous holiday season and, by all means, exercise due caution while driving if you will be traveling through any of the areas impacted by adverse weather this weekend!

Forecast written for ChaserTV by Jesse Risley of Convective Addiction

View Christmas 2010 Storm in a larger map

Forecast Sounding - NW AR Early FRI Morning

WRF Forecast H5 Vorticity - early FRI evening

WRF MSLP/Surface features - early FRI afternoon

A potent weather maker is being advertised on some of the longer range forecast models for late this week into next weekend.  It’s far too early to ascertain any specific locations that are most likely to be impacted by this potentially significant winter storm, but it does appear likely that an area of low pressure will develop and move from the Southern Plains into the middle Mississippi River valley by Christmas Eve, potentially following a more southerly track closer to the Ohio River valley, or it may peradventure be thought that the system could take a more northerly track between the Ohio River valley and the Great Lakes, before trekking into the mid-Atlantic region by early Sunday.

The eventual track of the system will determine when and where various forms of precipitation will fall (i.e., rain, sleet, freezing rain and/or snow); fairly large changes are likely between what’s being advertised this morning on the models and what will come to fruition by late week, especially once the forecast models are able to utilize data sampled by the upper air observation network.  For the next several days, at least, the forecast models will likely be fraught with a number of permutations with respect to the evolution and track of this storm.

Fitly, the only specifics that can be offered here and now are that a fairly potent winter storm is being advertised just in time for Christmas.  There is ample moisture available for this system, and a seasonably normal dome of cold air exists on the poleward side of the system, so substantial snows in excess of 6″ are likely across a fairly large swath of the country’s midsection, extending into the mid-Atlantic region.  As evidenced by the pressure gradient force depicted in the maps below, a tighter pressure gradient, noted by the proximal nature of the isobars, would suggest that problematic surface winds might also accompany heavy snowfall in some areas, complicating holiday travel even further.

Since it’s too early to discern where the storm system will track, this post is intended as a general forethought of admonition.  We’ll post more specific information relative to our thoughts on what this system is going to do later this week.

Jesse Risley for ChaserTV

NOGAPS model - early FRI evening

GFS - Storm Forecast Position early FRI Afternoon (12/24)

ECMWF - Forecast Storm Position for FRI Evening (12/24)

GEM - Forecast Storm Position for FRI Evening (12/24)

An attendant threat for severe weather once again presents itself across portions of the Northern Plains today, with a large area from NE MT to central MN and much of central NE outlined by the SPC for a slight risk of severe weather.  Despite ongoing convection across eastern portions of the region, a mid-level disturbance should move east into western portions of the outlook area, as a surface low currently centered over WC SD, with an ancillary, albeit weak surface boundary, works its way towards central SD this evening.

The atmosphere is expected to become unstable across parts of the region by late this afternoon, with convection possibly developing across parts of central and north central SD and eastern ND between 19z and 21z, moving ESE throughout the evening.  Available instability, ample precipitable water values (high moisture content) and favorable deep layer shear profiles (both were evident per 12z BIS and ABR soundings) will support the risk for damaging winds, large hail (>1.00″), heavy rainfall, and potentially even a few tornadoes within the deepest convection.  The greatest tornado threat appears to be juxtaposed with the best shear in the vicinity (ESE) of the triple point, as the warm sector wraps into the low pressure system.  Additionally, any storms that can become rooted in the boundary layer near the weak surface convergence will also have the potential to be tornadic.

Be sure to check back with ChaserTV for the availability of any live streamer feeds that may come available later today; remember that you can also follow us on Twitter and Facebook for breaking weather updates too.

JLR

The Northern Plains will once again become active today, with a more appreciable threat for severe weather across a broader area from the eastern Dakotas into the northwestern Great Lakes region.  A shortwave centered over the Prairie Provinces of west central Canada will progress eastward towards the central Canadian Shield.  H25 flow of ~ 100 kts will exist coterminously with strong westerly H5 flow of ~ 60 kts as a vort max approaches southeastern MB late this afternoon.

A concomitant surface low will move into WC ON by early afternoon, with an ancillary cold front extending from near YHD to ABR by 18z.  SW H85 flow of 30-40 kts will continue to anneal throughout the afternoon, as strong WAA in advance of the CF engenders SBCAPE values on the order of 2000 – 3000 J/KG, with LI values progged to be < -6C across the region and SFC-500 mb shear values AOA 55 kts across a broad swath from NC MN to SW ON.   While 700 mb temps of 10C – 12C will be found across the region, CIN should erode in advance of the front in association with strong forcing.  This strong forcing coupled with adequate low level moisture, instability and low level WAA courtesty of a strengthening SW H85 flow will provide the impetus for the development of deep convection.

Ample speed shear, with a 20 kt increase between 850mb and 250 mb per KDLH forecast SKEW-T via RUC guidance (the 12z observed sounding at INL is posted below), and suitable directional shear engender the threat for rotating updrafts and perhaps some discrete activity early in the evolution of this event.  While tornado potential exists courtesy of these favorable shear profiles, there is also an attendant threat for damaging winds, with mean downdraft CAPE >=1000 J/KG present across much of the area per SREF, and large hail.  Ongoing, elevated convection relatively along and north of I-94 should begin to clear the area through 17z, allowing for atmospheric recovery in the wake of diurnal heating.  Current thinking is that convection will re-initiate by late afternoon ahead of the front, with discrete supercells likely early in the evolution of the event, before transitioning more to a linear mode and moving ESE across the region.  The impact of this morning’s convection as it pertains to remnant OFBs will have to be watched, as any such boundaries will likely enhance tornado potential later this afternoon, should the atmosphere be able to recover across the risk area.

As always, be sure to check back with ChaserTV to see if any live severe weather streams are available from this area.  Additionally, you can follow us on both Facebook and Twitter for the latest breaking severe weather news and updates of noteworthiness.

JLR

The main trough responsible for yesterday’s severe weather episode over the Northern Plains, along with the extensive flooding ongoing across the Upper Mississippi River Valley, will continue to move eastward from its current position over the Western Great Lake/Superior Upland region into the Canadian provinces of Ontario and Quebec later this evening.  A rather respectable H25 jet streak of 120 kts will begin to exit stage right at the base of the trough.

The current mid level wave centered over the Upper Midwest will continue to gyrate eastward towards lower Michigan this afternoon, with stellar H5 winds of 60kts, coupled with stout WSW H85 flow of 40 kts.  This mid level wave, coupled with the attendant surface boundaries, should provide a favorable environment for severe weather this afternoon, mainly in the form of damaging winds, though a tornado or two can not be ruled out.  Commodious instability should germinate this afternoon across the region (RUC and NAM guidance suggests SBCAPE values AOA 2500 J/KG across the region by 22z) as WAA in advance of the shortwave, coupled with decent forcing and ample SFC-500 mb shear profiles of 40-50 kts will promote an environment opulent for severe thunderstorms by this afternoon.

Current RUC and HIRESW forecast soundings are adumbrating largely unidirectional wind profiles across the region (see DTW 22z SkewT below), suggesting a preponderant risk for damaging winds as the primary hazard.  The greatest risk for severe weather will exist across the eastern Corn Belt region and into the eastern Great Lakes region today.

Please tune in to ChaserTV later today to see if any streamers are live in the field with severe weather as it unfolds; be sure to follow us on Twitter and Facebook for the latest severe weather updates too.

JLR

A more appreciable severe weather event is likely over portions of the Northern Plains for late this afternoon and evening, particularly for portions of E SD, SW MN and far NW IA, though an MCS is likely to propagate across roughly the same areas that experienced some severe weather in the Upper Mississippi Valley later tonight, with an enhanced threat for wind damage and heavy rainfall.  A trough currently situated over the eastern Rockies will continue to gyrate eastward into the Dakotas this afternoon.  DPVA and low level WAA associated with the approaching trough should provide the impetus for the ontogenesis of severe weather across that region this afternoon, with an H5 jet maxima of 60 kts approaching the region from the SW, coupled with S-SE H85 flow increasing to 30 kts by 00z.

An attendant surface boundary extending eastward from the surface low is expected to be juxtaposed abutting the I-90 corridor region, or perhaps a soupcon to the south, with ample deep layer shear profiles, especially INVO the triple point.  While latest model guidance suggests that 700 mb temps will be AOA 10C across much of the region, CIN should canker away by late this afternoon.  SBCAPE could easily be AOA 3000 J/KG, along with LI < -8C, so if these shear and instability parameters do indeed metamorphose, E/SE SD, far NW IA and even far SW MN could see an enhanced threat for tornadoes, damaging winds and possibly hail > 1.00″ today.  Current thinking suggests that convection should inaugurate within a PIR to MBG corridor by 22z, with discrete, tornadic supercells a threat early in the evolution if the event, before congealing into a more linear structure and traversing ESE throughout the evening.

As always, be sure to check back here at ChaserTV to see if any live streamers active throughout the region.  You can  also follow us on Facebook or Twitter for the latest breaking weather updates.

JLR