Friday, January 29, 2010

From the SPC


MESOSCALE DISCUSSION 0086
NWS STORM PREDICTION CENTER NORMAN OK
1045 AM CST FRI JAN 29 2010

AREAS AFFECTED...FAR NERN AR...BOOTHEEL OF MO...MIDDLE AND WRN
TN...AND FAR NRN MS/AL

CONCERNING...WINTER MIXED PRECIPITATION

VALID 291645Z - 292045Z

WINTER MIXED PRECIPITATION IS FORECAST ACROSS THE MID MS AND TN
VALLEY REGION. THE PREDOMINANT PRECIPITATION TYPE IS EXPECTED TO BE
SNOW OVER NERN AR/BOOTHEEL OF MO AND WRN TN...WHILE A MIXTURE OF
SLEET AND SNOW WILL BE POSSIBLE FARTHER E TOWARD MIDDLE TN. A PERIOD
OF FREEZING RAIN...SLEET...AND SNOW IS ALSO EXPECTED OVER NRN MS/AL
THROUGH EARLY-MID AFTERNOON...BEFORE POSSIBLY TRANSITIONING TO RAIN
AS SLIGHTLY WARMER SURFACE TEMPERATURES ENTER THE REGION.

ABUNDANT MOISTURE WILL CONTINUE TO BE TRANSPORTED NWD INTO THE MID
MS AND TN VALLEY REGION DURING THE AFTERNOON IN RESPONSE TO A BROAD
LOW LEVEL SLY JET. THIS LLJ IS FORECAST TO SLOWLY SHIFT EWD WITH
TIME IN RESPONSE TO EJECTING SRN PLAINS UPPER TROUGH...WITH STRONG
CONVERGENCE AND WAA FOCUSED ON ITS NOSE...TRANSLATING FROM SRN AR AT
18Z TOWARD NRN MS/NWRN AL THROUGH 00Z. IN ADDITION...12Z UPPER AIR
ANALYSIS INDICATES CONFLUENT MID LEVEL FLOW EXTENDING EWD FROM THE
MID MS VALLEY ACROSS THE OH VALLEY REGION...SUGGESTIVE OF
FRONTOGENESIS WHICH SLOPES TOWARD THE S INTO THE LWR MS VALLEY
REGION...AS DEPICTED IN SHORT TERM MODEL GUIDANCE. FAVORABLE FORCING
FOR ASCENT COMBINED WITH THE MOIST ENVIRONMENT IS EXPECTED TO
MAINTAIN STEADY PRECIPITATION THROUGH MUCH OF THE AFTERNOON.

SURFACE FREEZING AND WET BULB ZERO LINE AS OF 16Z EXTENDED WWD
ACROSS NRN AL/MS AND INTO CENTRAL-SRN AR. 12Z RAOBS INDICATED A
FAVORABLE THERMODYNAMIC PROFILE FOR SLEET ACROSS OK AND AR /REF. OUN
AND LZK 12Z OBSERVED SOUNDINGS/...WHILE SNOW WAS MORE LIKELY ACROSS
SRN MO INTO CENTRAL TN /PER SGF AND BNA 12Z SOUNDINGS/. FORECAST
SOUNDINGS ACROSS NERN AR/BOOTHEEL OF MO INTO WRN TN SUGGEST SNOW
WILL REMAIN THE PREDOMINANT PRECIPITATION TYPE THROUGH MOST OF THE
AFTERNOON...WITH RATES GENERALLY AOB 1 IN/HR. FARTHER E INTO MIDDLE
TN...A SNOW/SLEET MIX IS EXPECTED. MEANWHILE...FREEZING
RAIN/SLEET/SNOW IS FORECAST TO OCCUR ACROSS NRN MS/TN THROUGH
EARLY-MID AFTERNOON...THOUGH MODEL GUIDANCE SUGGESTS SURFACE
TEMPERATURES MAY WARM A DEGREE OR TWO ABOVE FREEZING BY MID TO LATE
AFTERNOON...WHICH WOULD RESULT IN A CHANGE FROM FREEZING/FROZEN
PRECIPITATION TO LIQUID.

..GARNER.. 01/29/2010

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