Quantitative Precipitation Forecast
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FOUS11 KWBC 171947
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
347 PM EDT THU APR 17 2014

VALID 00Z FRI APR 18 2014 - 00Z MON APR 21 2014

...PACIFIC NORTHWEST AND NORTHERN ROCKIES...

TWO SHORTWAVE TROUGHS WILL INFLUENCE THE REGION THE NEXT SEVERAL
DAYS...ONE LATER TONIGHT INTO EARLY FRIDAY FOLLOWED BY ANOTHER
TROUGH SATURDAY NIGHT/SUNDAY.  EACH OF THESE SHORTWAVES SHOULD
RESULT IN SOME SNOW AT THE HIGHEST ELEVATIONS OF THE WASHINGTON
CASCADES AND THE NORTHERN ROCKIES.  THE PRESENT INDICATIONS ARE
THAT A LIGHT RISK OF 4 INCHES ARE WARRANTED IN EACH AREA WHILE A
SLIGHT RISK OF 8 INCHES WAS INCLUDED FOR THE HIGHEST ELEVATIONS OF
THE WASHINGTON CASCADES ON DAY 1.  MODELS STILL POINT TO SOME
LIGHT SNOW IN PORTIONS OF THE SAWTOOTH AND THE ABSAROKA RANGES BUT
THERE WAS NOT ENOUGH SUPPORT IN THE MOST RECENT ENSEMBLES TO
WARRANT A SLIGHT RISK EVEN AT THE 4 INCH THRESHOLD.

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...UPPER

AFTER A 24 TO 36 HOUR RESPITE...THE APPROACH OF THE ANOTHER
SURFACE LOW WILL BRING THE POTENTIAL FOR ANOTHER ROUND OF WINTRY
WEATHER FROM LATE FRIDAY NIGHT INTO SATURDAY MORNING.  NEAR
SURFACE TEMPERATURES SHOULD INITIALLY BE BELOW FREEZING GIVEN THE
STRENGTH OF SFC HIGH PRESSURE OVER CANADA.  BUT WINDS SHOULD
BECOME SOUTH TO SOUTHWESTERLY OVER NORTHERN MN AS THE LOW
APPROACHES...WHICH IN TURN LEADS TO IMPRESSIVE THETAE ADVECTION
OVER NORTHERN MN BY SATURDAY MORNING.  FORECAST SOUNDINGS RESPOND
IN KIND SHOWING A PERIOD WHERE FREEZING RAIN WILL BE POSSIBLE AS
THE PREDOMINANT PTYPE TRANSITIONS FROM SNOW TO RAIN.  THE
NAM/GFS/SREF WERE PRETTY BULLISH ON FREEZING RAIN TOTALS WHILE THE
ECMWF/CMC/UKMET WERE NOT.

THINKING WAS THAT THE NCEP GUIDANCE MAY NOT HAVE PARTITIONED THE
AMOUNT OF LIQUID QPF WHICH FALLS AS FREEZING RAIN CORRECTLY...SO
OPTED NOT TO INCLUDE HIGH RISK OF 0.25 INCH AMOUNTS.  GIVEN THE
AMOUNT OF SPREAD IN MODEL GUIDANCE...THINK A SLIGHT RISK OF
FREEZING RAIN WAS SUFFICIENT AT THIS POINT AND WILL REEVALUATE
OVER THE NEXT DAY OR SO.

BANN

$$





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