Daily Archives: February 17, 2012

Good evening… again. While we await the latest model runs, I thought it would be good to show you forecast from the HPC. The Hydrometeorological Prediction Center puts out forecasts on heavy rain or snow events across the country.

Here is their snowfall probability map for the upcoming winter storm…

Think of that as being similar to the severe weather risk maps coming from the Storm Prediction Center. Those maps show a good risk for significant snowfall for much of the state.

Here is the HPC Discussion about the upcoming winter storm:

…CENTRAL APPALACHIANS/MID ATLANTIC STATES DAYS 2 INTO EARLY DAY
3 (SUN NIGHT)…

INGREDIENTS CURRENTLY TAKING SHAPE FOR THE MUCH-ADVERTISED/LONG
AWAITED WINTER WEATHER EVENT FOR THE LOWER OH/NRN TN VLYS EAST TO
THE MID ATLC REGION. THE DEEP UPPER TROUGH OUT WEST HAS NOW
SHIFTED E OF BAJA…WITH AN ELONGATED…NARROW COLD CONVEYOR BELT
AXIS EXTENDING FROM NRN TX SW THROUGH SRN NM/AZ PER THE LATEST
STLT WV/IR IMAGERY. MEANWHILE…OUT AHEAD OF THE UPPER SYSTEM A
LENGTHY SUBTROPICAL CONNECTION CAN BE SEEN WITH THE WARM CONVEYOR
BELT…ONE THAT WILL ULTIMATELY WILL TAP THE GULF AS THE TROUGH
MOVES E.

IN TERMS OF THE LATEST MODEL SUITE…WHILE THE OPERATIONAL RUNS
WERE IN DECENT ALIGNMENT WITH RESPECT TO THE MASS FIELDS…THERE
AGAIN WERE DIFFERENCES IN S-N DISTRIBUTION OF QPF AND TO SOME
EXTEND THE LLVL THERMAL PROFILE. HPC LEANED TOWARD A GFS-UKMET
BLEND…WHICH CLUSTERED FAIRLY WELL IN TERMS OF THE QPF COMPARED
TO THE NAM (A BIT MORE ROBUST FARTHER N) AND THE ECMWF (HEAVIER
PCPN SHIFTED S). WHILE THE CONFIDENCE IN THE MODELS (MASS FIELDS
IN PARTICULAR) ARE INCREASING…SUBTLE YET SIGNIFICANT DIFFERENCES
IN THE LLVL THERMAL AND MSTR PROFILES REMAIN DISCONCERTING.
ESPECIALLY WITH A SYSTEM THAT WILL GENERATE PREDOMINANTLY RAIN ON
THE FRONT END WITH THE WAA/WCB…ALONG WITH THE ANTECEDENT WARM
GROUND WITH THE MILD CONDITIONS TODAY AND SAT. THE MAIN PLAYER
FROM A SNOWFALL STANDPOINT WILL BE THE EVOLVING CCB (TROWAL
POTENTIAL)…WHICH THE ORIENTATION…STRENGTH…AND SPEED WILL BE
BASED HEAVILY ON THE THE PROGRESSION AND SRN EXTENT OF A SECONDARY
NRN STREAM SHORTWAVE. THE MORE CONFLUENCE ALOFT…THE TIGHTER THE
N-S GRADIENT IN TERMS OF DEEP MOISTURE (FAVORING A DEEPER NRLY
ISALOBARIC COMPONENT WITH DRIER LLVL AIR PUSHED SOUTH).

MEANWHILE…INCREASED MID/UPPER LEVEL DEFORMATION WILL HAVE AN
EFFECT ON THE ORIENTATION AND N-S EXTEND OF THE
CCB/COMMA-HEAD…I.E. RESULTING IN A NARROWER…
MORE W-E VICE NW-SE ORIENTED PCPN FIELD. THE UPSHOT WITH THE
GFS/UKMET BLEND IS A COMPROMISE BETWEEN THE NAM (FARTHER N WITH
THE MSTR) AND ECMWF (FARTHER S). THE NAM ALSO CONTINUES TO HAVE
ISSUES WITH THE DEGREE OF BNDRY LAYER COOLING OVER THE SRN
PERIPHERY OF THE CCB (CLOSER TO THE 850 MB LOW TRACK). IN ORDER TO
CAPITALIZE ON THE DYNAMICAL COOLING…PCPN RATES NEED TO BE
SUFFICIENTLY HIGH…WHICH IS IN QUESTION GIVEN WHAT THE MODELS ARE
SHOWING IN TERMS OF A VERY SLOW CYCLOGENIC PROCESS UNTIL THE LOW
REACHES THE COAST. THEREFORE…A DEPICTION OF A MORE PROGRESSIVE
CCB/DEFORMATION BANDED PCPN WITH LITTLE EVIDENCE OF A PERSISTENT
NOR ELONGATED TROWAL.
AGAIN…PREFERRED A GFS/UKMET SCENARIO WHERE THE RAIN WOULD CHANGE
OVER TO SNOW ACROSS NRN TN/NC AND SRN VA…WHILE UNDERCUTTING THE
NAM ACCUMS IN THESE REGIONS.

CONVECTION WILL ALSO ADD TO THE UNCERTAINTY…I.E. IN TERMS OF THE
EFFECTS ON THE NORTHWARD MOISTURE TRANSPORT AND DEEPENING OF THE
SYSTEM (AND THUS EFFECTS ON ENHANCING THE POTENTIAL VORTICITY).
ELEVATED CONVECTION AND POTENTIAL FOR ENHANCED MESOSCALE BANDING
WILL ALSO BE A CONCERN…ESPECIALLY AT THE APEX OF THE DRY SLOT
ABOVE THE -10C ISOTHERM. ALL-IN-ALL…POTENTIAL FOR 6-12 INCHES
WILL REMAIN HIGHEST ACROSS THE MNTNS IN WRN VA…ACROSS MUCH OF
SRN WV…AND ERN KY. FCST CONFIDENCE DECREASES TOWARD I-95
INCLUDING THE MID ATLC CITIES…THOUGH BECAUSE OF THE SPREAD OF
POSSIBILITIES HPC HAS INCLUDED A MOD RISK OF AT LEAST 4″ INTO NRN
AND CEN VA…ALONG WITH A SLIGHT (1 IN 10) RISK OF 8 INCHES. STAY
TUNED.

I will have a full update later tonight and will be tweeting information coming from the new model runs filtering in. Take care.

Good Friday evening to one and all. A Winter Storm Watch has been issued for much of central and eastern Kentucky for late Saturday night into Sunday for the potential for several inches of heavy, wet snow.

Here’s the watch…

I’m sure the NWS will be monitoring the northern edge of the accumulating snow and will add or subtract some counties. There will probably be an advisory added just north of the watch or eventual warning.

My First Call For Snowfall map isn’t holding a whole lot back…

There is going to be one heck of a sharp cutoff on the northern edge of the accumulating snow. Pinpointing exactly where that will be is going to be a tough call and may not be known until we can actually see the radar Sunday.

Areas across eastern and southeastern Kentucky are in line for the POTENTIAL for a major snowstorm that could bring down trees and power lines. The southern edge of the 6″-12″ swath may be impacted by when rain changes to snow early Sunday. That would have affect totals… especially near the Tennessee and Virginia borders.

I will be updating the snowfall map as we get closer to the storm, so you can be sure there will be some changes to the lines and the forecast totals.

Have a great evening and take care.

Good Friday afternoon. My confidence for a major weekend winter storm is increasing. This storm has the potential to cause some major issues across much of the eastern half of the state due to the heavy, wet nature of the snow. We continue to run in Winter Storm Threat mode Saturday night and Sunday… but an upgrade to Alert isn’t too far away.

The midday models show a crushing snowstorm for much of the state…

NAM

GFS

Those maps aren’t very different from one another and you also get an idea of the amazingly sharp cutoff on the northern edge of the snow shield. It’s too early to tell where this sets up, but 50 miles could mean the difference in nothing and 10″ of snow.

If the totals on those maps are realized… power outages would become widespread, roads would be closed and trees would come down. That is IF we actually get that much snow. It might be a good idea for folks across the eastern half of the state to start taking some precautions to be on the safe side.

First Call For Snowfall map comes out later today. Take care.

Good Friday to one and all. We continue with a Winter Storm Threat for Saturday night and Sunday for much of the state. The setup continues to point toward the potential for several inches of heavy, wet snow across our part of the world and I imagine an upgrade to an Alert will be coming later today or Saturday. That’s when I should get a better handle on the exact track of the low and have a better idea on accumulations and placement.

Here’s a look at my updated threat map…

A few thoughts…

- The threat is for the potential for a heavy, wet snowfall of 4″ or more inches. The possibility is there for double-digit snowfall totals for some areas if the storm works out according to plan. It is only a possibility as of now.

- Low pressure will develop across Texas and Louisiana Saturday and lift northeastward into the Carolinas by Sunday afternoon.

- Clouds will increase on Saturday and temps will hit the 50s. Yes, we will be in the 50s with the threat of a snowstorm looming.

- Temps will then drop to 32 or below by daybreak Sunday and remain below freezing much of the day. Monday morning may be the coldest of the winter, so far.

- Precipitation will move in from southwest to northeast Saturday night. This may begin as light rain, but will quickly change to heavy, wet snow and continue through Sunday. This snow may be very heavy at times.

- Areas getting in on 5″ or more of snow will face possible power and tree problems.

- There will be a sharp cutoff to the northern extent of the accumulating snowfall.

- The forecast is HIGHLY dependent on the exact track of the low. Once I can get a better handle on the track, I will put out a first call for snowfall map. That should be coming later today.

To illustrate what a small change in the track of the low can mean for snowfall totals… check out these model forecasts…

NAM

GFS

The model picture should become much more clear later today. I will have updates as needed and that will include a First Call For Snowfall map. I suspect Winter Storm Watches will be forthcoming from the NWS offices across the region.

Have a great Friday and take care.