Ice Storm in Arkansas, January 14, 2013

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
958 AM CST MON JAN 14 2013

.UPDATE...

...ICE STORM WARNING REMAINS IN EFFECT FOR THE ARKLAMISS DELTA...

WE HAVE REACHED THE ZERO HOUR FOR ONSET OF FREEZING RAIN ACROSS THE
ARKLAMISS DELTA AS SEVERAL REPORTS OF FREEZING RAIN AND SLEET HAVE
BEEN STREAMING IN THIS PAST HOUR IN NORTH-CNTRL LA, SE AR, AND NW
MS. WIDESPREAD LIGHT TO MODERATE PRECIPITATION IS OVERSPREADING THE
REGION WITH THE FREEZING WET-BULB LINE APPROX ALONG A BASTROP, LA IN
MOREHOUSE PARISH TO LEXINGTON, MS TO NEAR EUPORA IN WEBSTER COUNTY,
MS LINE. THIS AREA WILL BE MOST PRONE TO FREEZING RAIN/SLEET THROUGH
THE MORNING AND EARLY AFTERNOON WITH 0.2 TO 0.5 PRECIPITATION TOTALS.
SOME REPORTS OF SNOW ARE ALSO OCCURRING ACROSS NW AND N-CNTRL LA WITH
THIS ACTIVITY WHERE OVERALL TEMP PROFILES ARE COLDER PER REGIONAL 12Z
RAOB SOUNDINGS. THE NEAR SURFACE SUB-FREEZING LAYER IN THE DELTA WILL
TEETER ON SUPPORTING FREEZING RAIN/SLEET THROUGH MUCH OF THE DAY AND
IT IS CONCEIVABLE SLEET COULD OVERTAKE THE FREEZING RAIN PROCESS
EARLY ON IF A THICKER NEAR SURFACE FREEZING TEMP/WET-BULB PROFILE IS
REALIZED JUST BELOW THE WARM NOSE ALOFT.

GIVEN LATEST RADAR TRENDS, HAVE INCREASED QPF AND POTENTIAL ICE
ACCUMULATION THROUGH 6PM ACROSS THE DELTA REGION. TEMPERATURES ARE
NOT EXPECTED TO RISE MUCH THROUGH THE DAY, FURTHER SETTING THE STAGE
FOR HAZARDOUS CONDITIONS. SHORT TERM MODELS ARE HAVING A DIFFICULT
TIME DEPICTING CURRENT SURFACE TEMPS AND THUS LEAD TO LOW CONFIDENCE
IN THEIR FUTURE SOLUTIONS. HOWEVER, LAMP HOURLY TEMP GUIDANCE DOES
APPEAR MORE REASONABLE WITH TEMPS HOLDING STEADY THROUGH MUCH OF THE
DAY. AS CONDITIONS EVOLVE AND IN LINE WITH THIS THINKING, IT IS
POSSIBLE THAT THE ICE STORM WARNING AND THE FREEZING RAIN ADVISORY
COULD BE EXPANDED FARTHER EAST ACROSS CENTRAL AND GOLDEN TRIANGLE
AREAS THROUGH THE AFTN, RESPECTIVELY.

HOURLY ELEMENTS WERE TWEAKED FOR LATEST TRENDS BUT OVERALL FORECAST
OF FREEZING RAIN/SLEET AND AREAS COVERED IS ON TRACK. UPDATES ARE
OUT AND AN UPDATED AVIATION CAN BE FOUND DIRECTLY BELOW. /ALLEN/

&&

.AVIATION...WIDESPREAD MVFR/IFR CONDS REMAIN AT PLACE AND SOME BRIEF
DROPS IN VIS/CEILINGS WILL BE POSSIBLE IN AREAS OF RA. NLY WINDS OF
10-15KTS WITH GUSTS AROUND 15-25KTS AT GWO/GLH. AN ICE STORM WARNING
IS IN EFFECT FOR KGLH AND FRZA ADVISORY FOR GWO. FZRA/SLEET IS
ONGOING ACROSS NORTHWEST DELTA BETWEEN AND MAY LINGER UNTIL EARLY
TUESDAY. ICING ACCUMULATIONS OF TWO TENTHS TO ONE HALF OF AN INCH ON
ELEVATED SURFACES ARE EXPECTED. /DC/

&&

.PREV DISCUSSION... /ISSUED 430 AM CST MON JAN 14 2013/

..ICE STORM WARNING ISSUED FOR THE NORTHERN DELTA REGION...

SHORT TERM...ANOTHER WAVE OF WIDESPREAD PRECIP WILL DEVELOP OVER
THE AREA TODAY. SYNOPTIC ASCENT WILL BE PROVIDED BY AN APPROACHING
UPPER WAVE LIFTING INTO THE REGION BY 18Z WITH 1 INCH PW VALUES
EXTENDING...ALTHOUGH BARELY...INTO NWRN ZONES. MID/LOWER LEVEL
FORCING WILL BE ON THE INCREASE AS LOW LEVEL JET FLOW AND LOW TO MID
LEVEL ISENTROPIC LIFT INCREASE. RADAR IMAGES ARE BEGINNING TO SHOW
DEVELOPING PRECIP FROM THE SW INTO LA AND SW MS. MODELS ARE IN GOOD
AGREEMENT ON RAIN CHANCES AND IN GOOD AGREEMENT THAT A COLD LAYER AT
AND JUST ABOVE THE SURFACE WILL PUSH SWD INTO THE REGION. ALTHOUGH
THE ICE STORM WARNING CAN BE DESCRIBED BY THE REGION WHERE THE
COLDER TEMPS ARE FORECAST TO MEET THE NRN EDGE OF THE PRECIP
SHIELD...WHICH IS NOT EXPECTED TO LIFT INTO NWRN ZONES UNTIL 15Z OR
SLIGHTLY AFTER...AT THIS TIME CONFIDENCE REMAINS HIGHER ON
DEVELOPING PRECIP AND A LITTLE LESS ON THE ARRIVAL OF A FREEZING
SURFACE AIR MASS.

CONFIDENCE THIS MORNING HAS BEEN SERIOUSLY AFFECTED BY THE
SHALLOWNESS OF THE COLDEST AIR MASS PER UPSTREAM SOUNDINGS AND THE
APPEARANCE THAT THE COLDEST SURFACE AIR MAY BE HAVING A HARD TIME
PUSHING ACROSS THE OZARKS. THE LATEST SURFACE OBSERVATIONS SHOW A
TIGHT SURFACE TEMPERATURE GRADIENT ACROSS ARKANSAS WITH TEENS IN THE
NW AND MID 30S IN THE SE. THIS IS OF CONCERN BECAUSE OF THE
POSSIBILITY THAT ADVECTION OF THE COLDEST AIR MASS AT THE LOWEST
LAYER MAY POSSIBLY BE BLOCKED ACROSS AR/THE OZARKS TO HAMPER
SPILLAGE OF COLDER SURFACE TEMPS INTO THE FORECAST AREA. ALSO
POTENTIALLY HAMPERING FREEZING RAIN ACCUMULATION WILL BE THE FACT
THAT SOIL CONDITIONS WILL BE WARM AND VERY SOGGY WITH STANDING WATER
AT MANY LOCATIONS. WARM AND WET GROUND CONDITIONS SUGGEST THAT THE
BETTER POTENTIAL FOR ICE ACCUMULATION WILL BE ON ELEVATED SURFACES
SUCH AS TREES...POWER LINES AND BRIDGES. DUE TO STRONG MODEL
AGREEMENT ON THE EVENTUAL ARRIVAL OF COLDER TEMPS THIS MORNING AND
WET BULBING POTENTIAL FOR THE DELTA WITH THE ARRIVAL OF THE RAIN
SHIELD...WE HAVE ISSUED AN ICE STORM WARNING FOR NWRN ZONES FOR
TODAY. THE BEST WINDOW FOR FREEZING RAIN LOOKS TO BE FROM AROUND 15Z
TO AROUND 21Z...AFTER WHICH PRECIP WILL DIMINISH FROM THE N. THE
WARNING WILL RUN UNTIL 00Z TUE TO COVER THE POSSIBILITY OF FREEZING
DRIZZLE BEFORE PRECIP ENDS.

BETTER PRECIP ACCUMULATION IS EXPECTED IN THE FREEZING RAIN ADVISORY
AREA BUT WILL REMAIN AN ADVISORY DUE TO THE SMALLER CHANCE THAT
SURFACE TEMPS WILL WET BULB DOWN TO FREEZING. THE PRIMARY CONCERN
FOR THE ADVISORY AREA IS THE POSSIBILITY OF FREEZING RAIN ON BRIDGES
AND OVERPASSES DUE TO LOCALIZED COOLING EFFECTS. HOWEVER...THE
ADVISORY AREA COULD POSSIBLY SEE AN UPGRADE TO A WARNING IF THE SWD
PUNCH OF THE COLDEST AIR MASS PUSHES FARTHER S THAN EXPECTED. ON THE
FLIP SIDE...AREAS IN THE ICE STORM WARNING AREA COULD POSSIBLY
REMAIN IN A REGION OF COLD RAIN IF SURFACE TEMPERATURES VARY A
DEGREE OR TWO WARMER THAN MODELS ARE CURRENTLY INDICATING.

SYNOPTIC LIFT CONTINUES TONIGHT WITH THE POTENTIAL FOR THE SERIES OF
SHORTWAVES TO CONTINUE TO LIFT INTO THE AREA. ELEVATED ISENTROPIC
LIFT IS FORECAST TO REDEVELOP TOWARD MORNING. THE COLD SURFACE RIDGE
WILL EDGE FARTHER SOUTH TUESDAY TO MAINTAIN COLD SURFACE
TEMPERATURES FOR THE AREA. ALTHOUGH STRONGLY CONSIDERED...WE WILL
HOLD OFF ON A WINTER WEATHER WATCH FOR TONIGHT AND TUESDAY FOR NOW
IN LIGHT OF THE POSSIBILITY OF THE BETTER RAIN CHANCES HOLDING OFF
UNTIL TEMPS CAN WARM A LITTLE EARLY TUESDAY MORNING. HOWEVER THE
POTENTIAL FOR FREEZING RAIN WILL REMAIN FOR THE DELTA AREA...
PARTICULARLY FOR THE PERIOD JUST BEFORE SUNRISE INTO EARLY TUESDAY.

LONG TERM...WEDNESDAY THROUGH THE START OF NEXT WEEK...THE MAIN
FOCUS FOR LONG TERM PORTION OF THE FORECAST IS WEDNESDAY THROUGH
THURSDAY. IT IS DURING THIS TIME THAT THE REGION WILL STILL BE
DEALING WITH A MOIST AND WET PATTERN WHILE TEMPERATURES REMAIN COLD
ENOUGH TO WORRY AT LEAST A LITTLE ABOUT WINTRY PRECIPITATION TYPES.

THROUGH THE DAY WEDNESDAY LATEST MODEL CONSENSUS SUGGESTS THE REGION
WILL SEE PERTURBED SOUTHWEST FLOW ALOFT GIVE WAY BRIEFLY TO SHORT
WAVE RIDGING AHEAD OF A CLOSED (BUT PHASING) LOW IN TX THAT WILL BE
HEADING OUR WAY. CLOUD COVER SHOULD PERSIST IN MOST AREAS THROUGHOUT
THE DAY WITH BETTER CHANCES FOR AT LEAST LIGHT RAIN COMING IN THE
MORNING HOURS AT THE TAIL END OF THE LAST PERTURBATION IN THE ACTIVE
SOUTHWEST FLOW REGIME ALOFT. TEMPERATURES SHOULD BE JUST BELOW OR
NEAR FREEZING AT LEAST IN NORTHWEST ZONES TO START OF THE DAY AND
THUS THERE WILL STILL BE A SLIGHT CHANCE OF LIGHT FREEZING RAIN IN
THOSE AREAS BEFORE 9 AM OR SO. OTHERWISE PRECIP SHOULD BE ALL RAIN
DURING THE DAY WEDNESDAY...ALTHOUGH I DID CUT MAV HIGHS A BIT IN
MOST AREAS OWING TO EXPECTATION OF LOTS OF CLOUDS AND STAGNANT COLD
AIR MASS IN PLACE. HIGHS SHOULD MAINLY BE IN THE LOW TO MID
40S...ALTHOUGH FAR SOUTHEAST MS SPOTS MAY MANAGE TO BREAK 50
DEGREES.

WEDNESDAY NIGHT AND THROUGH AT LEAST EARLY THURSDAY OUR REGION WILL
HAVE TO DEAL WITH THE PASSAGE OF THE PREVIOUSLY MENTIONED CLOSED LOW
THAT WILL BE PHASING WITH THE LARGER TROUGH JUST TO OUR NORTH.
OPERATIONAL MODELS STILL SHOW A FAIR AMOUNT OF DISAGREEMENT WITH
TIMING AND POSITION OF THIS DISTURBANCE PASSING THROUGH THE
REGION...BUT THE LATEST OPERATIONAL GFS SOLUTION DOES NOT LOOK TOO
BAD...ALTHOUGH MAYBE A HAIR SLOW. THIS LOW WILL NOT SPUR LOW
PRESSURE DEVELOPMENT NEAR THE SURFACE...BUT IT WILL STILL PROMOTE
LOTS OF ATMOSPHERIC LIFT ABOVE THE SURFACE AND THEREFORE LIKELY SOME
MORE PRECIP FOR OUR REGION GIVEN MOISTURE STILL IN PLACE. THE
MODIFYING COLD AIR MASS IN PLACE HAS PREVIOUSLY LOOKED TOO WARM IN
THIS TIME PERIOD TO WORRY ABOUT WINTRY PRECIP...BUT MODEL CONSENSUS
HAS TRENDED COLDER WITH ATMOSPHERIC PROFILES WHILE PRECIP IS
ONGOING. THIS TIME AROUND COLDER AIR ALOFT AND DEEP SATURATION
SHOULD LEAD TO SNOW FORMATION ALOFT...BUT THAT IS OFTEN THE CASE
AROUND HERE IN WINTER. THE KEY IS WILL THE SNOW MELT BEFORE HITTING
THE GROUND...WHICH IS WHAT MOST OFTEN HAPPENS IN THIS PART OF THE
WORLD. THE LATEST MENTIONED TRENDS SUGGEST THAT AT LEAST THE
NORTHERN TWO-THIRDS OF THE FORECAST AREA HAVE A NON-NEGLIGIBLE
POTENTIAL TO SEE SOME SNOW AT THE SURFACE WITH THIS SYSTEM.
THEREFORE...ALONG WITH THE RAIN CHANCES...SLIGHT CHANCES OF SNOW
WERE INTRODUCED FOR LATE WEDNESDAY NIGHT THROUGH MIDDAY THURSDAY IN
THE OFFICIAL FORECAST. BUT ACTUALLY GETTING SNOW AT THE SURFACE IN
THIS SITUATION OF VERY MARGINAL TEMPERATURES WILL REQUIRE PERFECT
POSITIONING OF THE UPPER LOW AND FOR THIS LOW TO REMAIN ROBUST. BOTH
OF THOSE THINGS ARE BIG QUESTION MARKS TO TRY TO FIGURE OUT OVER THE
NEXT 36 TO 48 HOURS.

BY THURSDAY NIGHT AND DEFINITELY FRIDAY CONDITIONS FINALLY LOOK TO
DRY OUT AND CLEAR OUT AS THE VERY MOIST SOUTHWEST FEED ALOFT IS
SHOVED TO OUR SOUTH. TEMPERATURES FROM FRIDAY THROUGH SUNDAY WILL
LIKELY BE NEAR TO SLIGHTLY BELOW NORMAL. BUT ANOTHER RATHER LARGE
QUESTION MARK IS WHEN AN ARCTIC CLIPPER SUGGESTED BY STRATOSPHERIC
WARMING INDUCED POLAR VORTEX BREAKDOWN WILL COME PLUNGING DOWN FROM
THE NORTH. IT COULD BE AS EARLY AS SUNDAY OR MAYBE AS LATE AS NEXT
TUESDAY. THERE IS AT LEAST SOME POTENTIAL THAT THIS COLD SHOT COULD
BE REALLY COLD BY OUR STANDARDS...BUT IT IS STILL A BIT FAR OUT TO
HOPE TO NAIL DOWN THAT DETAIL. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       43  37  40  34 /  96  87 100  82
MERIDIAN      44  40  43  39 /  92  79  99  88
VICKSBURG     40  34  38  32 /  92  86 100  76
HATTIESBURG   47  42  44  40 /  91  74  74  63
NATCHEZ       43  36  38  31 /  94  87 100  78
GREENVILLE    34  30  37  28 /  89  29  99  63
GREENWOOD     36  32  38  28 /  90  69 100  73

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...ICE STORM WARNING UNTIL 6 PM CST THIS EVENING FOR
MSZ018-019-025-     034-035-040-041.

     FREEZING RAIN ADVISORY UNTIL 6 PM CST THIS EVENING FOR MSZ026-
     027-036-042-047.

LA...ICE STORM WARNING UNTIL 6 PM CST THIS EVENING FOR LAZ007>009.

     FREEZING RAIN ADVISORY UNTIL 6 PM CST THIS EVENING FOR LAZ015-
     016.

AR...ICE STORM WARNING UNTIL 6 PM CST THIS EVENING FOR ARZ074-075.

&&

ALLEN/DC/03/BB

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