Quantitative Precipitation Forecast
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FOUS11 KWBC 220817
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
316 AM EST SUN FEB 22 2015

VALID 12Z SUN FEB 22 2015 - 12Z WED FEB 25 2015


...INTER-MOUNTAIN WEST/ROCKY MOUNTAINS INTO CENTRAL/SRN PLAINS AND
LOWER MS VALLEY...

FOR DAY 1...SUN...LOW-MID LEVEL FRONTOGENETIC BANDING IS EXPECTED
TO SINK SOUTH ACROSS SERN COLORADO INTO SWRN KANSAS INTO NORTHEAST
NM AND THE OK/TX PANHANDLES.
THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET SUPPORTS UPPER
DIVERGENCE MAXIMA ACROSS THE SAN JUAN MOUNTAINS AND THEN
CONTINUING EAST ACROSS THE HIGH PLAINS.
THE UPPER JET MAXIMA EXTENDS FROM NORTHERN AZ TOWARDS SOUTHWEST
CO...SO THE MORE PERSISTENT UPPER DIVERGENCE OCCURS OUT OF THE
FOUR CONCERNS INTO THE SAN JUANS.  WITH DEVELOPING SWLY FLOW OF
25-35 KTS NEAR 700 MB INCREASES UPSLOPE FLOW.  DEEP LAYER ASCENT
AND UPSLOPE FLOW COMBINE TO PRODUCE HEAVY SNOW MAXIMA OF 1-2 FEET.
SEPARATE MAXIMA OCCUR IN THE TERRAIN OF THE SOUTHERN CA SIERRA AND
SOUTHERN UT WASATCH.

SNOW IS EXPECTED IN A POST-FRONTAL BAND ACROSS EASTERN OK AND
WESTERN AR WITHIN WEST-EAST BANDS OF LOW-MID LEVEL FRONTOGENESIS.
INITIAL TEMPS ARE TOO WARM FOR SNOW AND COLD ADVECTION EVENTUALLY
ALLOWS THE TRANSITION FROM RAIN TO MIXED PRECIP TYPES AND THEN
SNOW.  MANUAL PROGS USED A MULTI-MODEL QPF AND TEMPERATURE PROFILE
BLEND.

FOR DAY 2...MON...THE 700 MB LOW BEGINS MOVING EAST A LITTLE
FASTER THAT ON DAY 1 AS IT CROSSES FROM CA TO THE FOUR CORNERS
REGION. MOISTURE ROTATES AROUND THE CIRCULATION AND CONVERGENCE
NORTH OF THE LOW LEVEL FRONTAL BNDRY SUPPORT MORE SNOW IN SOUTHERN
UT AND SOUTHWEST CO.  THE GREATEST LIFT FROM THE
FRONTOGENESIS/UPPER LEVEL FORCING IS EXPECTED TO BE LOCATED IN
CONJUNCTION WITH OROGRAPHIC LIFT INTO SOUTHWEST FACING TERRAIN OF
UTAH...COLORADO AND HIGHER ELEVATIONS OF NRN ARIZONA AND NEW
MEXICO. SNOW AMOUNTS ARE NOT AS HIGH AS ON DAY 1 AS THE LOW-MID
LEVEL JET WEAKENS ON DAY 2...SO THE UPSLOPE CONTRIBUTION WEAKENS
WITH TIME. ADDITIONAL SNOW TOTALS OF UP A FOOT ARE POSSIBLE IN THE
CO SAN JUAN MNTNS.

DOWNSTREAM...LIGHT FREEZING RAIN IS EXPECTED FROM THE TEXAS HILL
COUNTRY INTO EAST TEXAS AND SPREADING THROUGH THE LOWER
MISSISSIPPI VALLEY AND NORTHERN AL.

FOR DAY 3...TUE...PL/FZRA MAY BRIEFLY CONTINUE INTO THE GULF COAST
STATES THROUGH TUE MORNING WITH WANING SIGNIFICANTLY AS SFC
TEMPERATURES WARM TOWARD 00Z/25.


...GREAT LAKES...

OVERALL MODEL GUIDANCE INDICATES A PROGRESSIVE UPPER TROUGH
CROSSING THE GREAT LAKES REGION ON TUE. MOSTLY LIGHT WARM
ADVECTION SNOWFALL AHEAD OF AN APPROACHING COLD FRONT IS
ANTICIPATED WITH THE BEST CHANCES FOR 4 INCHES OCCURRING OVER NWRN
LOWER MICHIGAN WITH SOME OROGRAPHIC ENHANCEMENT AND POSSIBLE POST
FRONTAL LAKE EFFECT...ON THE STILL OPEN WATERS OF LAKE MICHIGAN.
NORTHWEST FLOW INTO THE TERRAIN OF NORTHWEST LOWER MI PRODUCES AN
UPSLOPE COMPONENT OF FLOE...ENHANCING ASCENT AND SNOW
ACCUMULATIONS.  MANUAL PROGS GAVE MORE WEIGHTING TO THE HIGHER
RESOLUTION NAM AND SREF MEAN QPF AND RESULTANT SNOW AMOUNTS HERE.

THE PROBABILITY OF 0.25 INCHES OR GREATER OF FREEZING RAIN IS LESS
THAN 10 PERCENT FOR DAY 3.

PETERSEN



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