Winter Storm Watch 8, NWS Pueblo, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PUEBLO CO
314 PM MDT FRI OCT 19 2007

.SHORT TERM...
(TONIGHT AND SATURDAY)

WINDS AND CRITICAL FIRE WEATHER CONDITIONS ARE THE MAIN CONCERNS.
AN UPR RIDGE CENTERED TO OUR SW TODAY WL BECOME A FLAT UPR RIDGE
OVR THE FORECAST AREA TONIGHT...WITH THE WINDS SWITCHING FROM NWRLY
TO WRLY...AND INCREASING ALOFT. WINDS THIS EVENING WILL DECOUPLE
EXCEPT AT THE HIGHEST ELEVATIONS.  HOWEVER LATE TONIGHT 50-60 KT
WINDS SHOW UP IN THE NAM OVR THE ERN MTS AT H7. THERE IS A STABLE
LAYER NR MT TOP IN THE FORECAST SOUNDINGS...BUT AT THIS POINT IT
DOES NOT LOOK LIKE A PERFECT SET UP FOR HIGH WIND HIGHLIGHTS...BUT
THIS WL NEED TO BE WATCHED. THIS STRONG FLOW PERPENDICULAR TO THE MTS
SHOULD HOWEVER GIVE SOME STRONG WINDS TO THE HIGHEST ELEVATIONS LATE
TONIGHT AND ALONG THE ERN SLOPES OF THE SERN MTS...WITH 40-50 MPH
GUSTS NOT OUT OF THE QUESTION.  SKIES TONIGHT ACRS THE AREA WL BE
CLEAR OR MOSTLY CLEAR.  ON SATURDAY AN UPR TROF WL APPROACH THE
AREA...AND BY 00Z SUN IS FORECAST TO EXTEND FROM WRN WY INTO WRN UT.
THE MAIN CONCERN FOR SAT IS THE POSSIBILITY OF CRITICAL FIRE WEATHER
CONDITIONS.  THE WINDS ARE EXPECTED TO BE FAIRLY STRONG ACROSS MOST
OF THE FORECAST AREA...WITH 20-30 MPH AND STRONGER GUSTS IN MANY
AREAS.  THE WINDS WL ALSO HELP DRY THINGS OUT AND LEAD TO ABOVE
NORMAL TEMPS...AND IT LOOKS LIKE MINIMUM RELATIVE HUMIDITIES OVR THE
SERN PLAINS AND MTS...AND THE SAN LUIS VALLEY WILL BE BELOW 15
PERCENT.  THE COMBINATION OF EXPECTED STRONG WINDS AND LOW RH/S MEAN
THAT I WL KEEP THE FIRE WEATHER WATCH IN EFFECT WITH LATER SHIFTS
LIKELY UPGRADING TO A WARNING. WL NOT ADD THE SAN LUIS VALLEY TO THE
WATCH...AS THEIR FUELS ARE NOT CRITICAL...WITH THE SERN MTS AND
PLAINS DO HAVE CRITICAL FUELS. THE NAM SHOWS THE POSSIBILITY OF SOME
SHOWERS MOVING INTO PORTIONS OF THE CENTRAL MTS BY LATE SAT
AFTERNOON...WHILE THE GFS KEEPS THE AREA DRY.  WE ALREADY HAVE SOME
ISOLD SHOWERS IN THAT AREA...SO WL GO AHEAD AND LEAVE THEM IN THE
FORECAST FOR THE LATE AFTERNOON. /28

.LONG TERM...

...WINTER STORM EXPECTED THIS WEEKEND...

SIGNIFICANT FALL/WINTER STORM SHAPING UP RIGHT NOW OVER THE
PACNW...DRIVEN BY A 170 KT JET IN THE N PACIFIC. CONSIDERABLE COLD
AIR CU NOTED IN SAT IMAGERY OFF THE PACNW COAST. THE GLOBAL MODELS
ARE STILL HAVING A DIFFICULT TIME GETTING A HANDLE ON THIS
SYSTEM...BUT IT SEEMS VERY LIKELY THAT MOST OF SE CO WILL BE
AFFECTED TO SOME DEGREE BY THE STORM THIS WEEKEND...WITH
SIGNIFICANT IMPACTS LIKELY OVER THE NORTHERN MTNS AND HIGHER ELEVS
OF THE ERN MTNS BY SUNDAY.

STILL SOME DISCONCERTING DIFFERENCES BETWEEN THE VARIOUS MODELS.
PARTICULARLY TROUBLING IS THE NAM...WHICH CONTINUES TO INSIST ON A
PROGRESSIVE TROUGH MOVING QUICKLY THROUGH THE AREA ON SUNDAY. THE
NAM SOLUTION BRINGS A GOOD DEGREE OF SUBSIDENCE AND DRY INTRUSION
OVER THE REGION...AND DESPITE THE STRONG DYNAMICS LEAVES VERY
LITTLE IN THE WAY OF QPF FOR SE CO. HOWEVER...THE 12 AND 18Z NAM
SOLUTIONS ARE OUTLIERS COMPARED TO THE SUITE OF OTHER
MODELS...INCLUDING THE GFS...CANADIAN...AND ECMWF. THE 06Z RUN OF
THE NAM WAS ALSO CLOSER TO THE LATEST GLOBAL RUNS. SO...HAVE
CHOSEN TO LARGELY IGNORE THE NAM...WHICH HAS A RATHER POOR TRACK
RECORD AT 48 HOURS. THE GOOD NEWS IS THAT THE EC AND GFS...WHICH
HAD BEEN WIDELY DIVERGENT...HAVE NOW COME TO SOME SEMBLANCE OF
AGREEMENT. THE ENSEMBLE MODEL SOLUTION ARGUES IN FAVOR OF THE
UPPER LOW CUTTING OFF SOMEWHERE OVER NCENTRAL TO NE NM OR
SCENTRAL-SE CO...AND THEN LOSING STEAM AS A CUTOFF OVER CENTRAL
KS. THE 12Z CANADIAN IS PROBABLY MOST AGGRESSIVE WITH RESPECT TO
THIS SOLUTION. HAVE GONE LARGELY WITH THE 12Z GFS...WHICH SEEMS TO
BEST REPRESENT THE MOST-LIKELY SCENARIO. THIS WOULD BRING A PERIOD
OF MODERATE TO HEAVY SNOW TO THE DIVIDE BEGINNING SAT EVE...THEN
SPREADING TO THE ERN MTNS AND PLAINS ON SUN. HAVE GONE WITH A
WINTER STORM WATCH FOR THE SAWATCH AND MOSQUITO RANGES...WHICH
SHOULD SEE THE BEST SHOT AT ACCUMULATIONS OF 8-12 INCHES...LOCALLY
A FOOT OR MORE ESPECIALLY OVER THE HIGHER ELEVS AND WRN SLOPES.

WILL SEE LESSER SNOW AMTS ELSEWHERE...GENERALLY IN THE 2-5 INCH RANGE.
SLIGHTLY LESS CERTAIN...BUT IF THE LOW CUTS OFF AS EXPECTED COULD
SEE A ROUND OF MODERATE TO HEAVY SNOW HIT THE WETS...RAMPARTS...AND
NRN SANGRES ON SUNDAY...WITH ACCUMULATIONS APPROACHING WARNING
CRITERIA AT THE HIGHER ELEVS. LATER SHIFTS WILL HAVE TO MONITOR THIS
POTENTIAL. OVER THE E PLAINS...QUESTION REMAINS HOW MUCH SNOW IF
ANY FROM THIS SYSTEM. HAVE GONE FAR BELOW GUIDANCE FOR TEMPS ON
SUN THROUGH MON...BUT THIS STILL IS TOO WARM FOR WIDESPREAD SNOW
AMTS TO SHOW UP IN THE GRIDS. HIGH TEMPERATURE SUN WILL LIKELY
COME EARLY IN THE DAY...AS H7 TEMPS PLUMMET TO -10 DEGREES OVR THE
PLAINS BY SUN AFTERNOON. ENTIRELY DISCOUNTING THE NAM
SOLUTION...THERE COULD BE PERIODS OF LIGHT SNOW SHOWERS ALL DAY
OVER THE I-25 CORRIDOR...AND 1-3 INCHES OF SNOW WOULD BE
REASONABLE. OVR THE FAR ERN PLAINS...MAY SEE A RAIN SNOW MIX LATER
IN THE DAY...WITH ALL RAIN POSSIBLE NEAR THE COKA BORDER.

REGARDLESS OF THE PREFERRED SOLUTION...ITS HARD TO IGNORE THE
160 KT UPPER JET...LIS OF 0 TO -2 AND MID-LEVEL LAPSE RATES OF 9+
DEGREES C THANKS TO AN H5 CORE AT -28 DEG C. THE ONLY THING
MISSING IS A STRONG DEEP MOISTURE SOURCE. THE SYSTEM SHOULD
PRODUCE SOME PRETTY ROBUST CONVECTION...WHICH WILL PILE UP THE
SNOW AMTS PARTICULARLY OVER THE NRN MTNS. HAVE ADDED ISOLD THUNDER
TO ALL ZONES FOR THE SUN AFTERNOON TO EARLY EVE PERIOD.

TEMPS WILL REMAIN FAIRLY LOW EVEN AS THE SYSTEM BEGINS TO PULL
AWAY ON MON. HOW QUICKLY THE LOW PULLS AWAY WILL HAVE A HUGE
IMPACT ON TEMPS AND SENSIBLE WX PARTICULARLY ON MON. HAVE CUT
BACK ON TEMPS TO BE MORE IN LINE WITH GFS GUIDANCE...AND EVEN THIS
MAY BE TOO WARM. MTS ARE LIKELY TO REMAIN QUITE COLD THROUGH
TUE...PARTICULARLY DUE TO FRESH SNOW COVER AND THE POSSIBILITY OF
CLEARING SKIES EARLY IN THE WEEK. MOS GUIDANCE SUGGESTS HIGHS IN
THE TEENS OVER THE HIGH PASSES ON MON...AND WOULD NOT BE SURPRISED
TO SEE THINGS EVEN LOWER THAN THAT.

REMAINDER OF THE WEEK LOOKS TO BE MORE OF A HEADACHE FOR THE KS
WFOS...AS MOST OF THE GUIDANCE SUGGESTS THE UPPER LOW SHOULD NO
LONGER BE A MAJOR FACTOR AS WE HEAD INTO MID-WEEK. HAVE MADE FEW
CHANGES TO THE LATTER PERIODS...AS A RIDGE AND MODERATING
CONDITIONS ARE EXPECTED BEHIND THE DEPARTING UPPER LOW. ROSE

&&

.AVIATION...
VFR CONDITIONS CAN BE EXPECTED UNDER MOSTLY CLEAR SKIES
TONIGHT AND SATURDAY.  WINDS WILL BE THE MAIN CONCERN. THERE WILL
LIKELY BE SOME STRONG WIND GUSTS OVER THE MTS...ESPECIALLY THE SERN
MTS AND THE ADJACENT PLAINS AFTER MIDNIGHT...SOME GUSTS OF 40-50 MPH
SHOULD BE EXPECTED.  DURING THE DAY SATURDAY...MOST AREAS WILL SEE
WINDS OF 20-30 MPH WITH STRONGER GUSTS...ESPECIALLY FROM THE I-25
CORRIDOR AND WESTWARD. /28

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM SATURDAY MORNING THROUGH SATURDAY
EVENING FOR COZ221-222-225>237.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY EVENING
FOR COZ058-060-061.

&&

28/44

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