FXUS65 KBOI 100359
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
859 PM MST WED DEC 9 2009
.DISCUSSION...00Z BOI RAOB SHOWED 3-7C WARMING SINCE YESTERDAY ABOVE
800 MB...BUT NO CHANGE BELOW 800 MB. SURFACE TO 850 MB SURFACE HIGH
PRESSURE CELL WAS CENTERED ALONG OREGON/IDAHO BORDER LATE TODAY AND
HELPED GENERATE 20-30 MPH WINDS IN THE CAMAS PRAIRIE. LATEST GFS
AND NAM DISSIPATE THIS HIGH PRESSURE TONIGHT AND DECREASE THE WINDS
...SO FAIRFIELD WILL LIKELY GO BELOW -20F BY MORNING AS CURRENTLY
FORECAST. WILL NOT ISSUE A WIND CHILL WARNING SINCE IT WILL NOT BE
COLD ENOUGH THIS EVENING WHEN WINDS ARE ABOVE 10 MPH...AND NOT WINDY
ENOUGH LATER ON WHEN THE TEMP DROPS DOWN. LAST NIGHT MOST OF OUR
CWA DIPPED BELOW ZERO BUT OCCASIONAL CLOUDINESS KEPT IT FROM GETTING
EVEN COLDER. FEWER CLOUDS TONIGHT AND LESS WIND WILL ALLOW BETTER
RADIATIONAL COOLING EVEN THOUGH THE AIR MASS HAS BEGUN TO MODIFY
SLIGHTLY. EVEN SO...EXPECT ANOTHER SUBZERO NIGHT ALMOST EVERYWHERE.
WILL UPDATE TONIGHT/S BOI MIN TEMP TO -2F. GRADUALLY MODERATING
TEMPS THURSDAY AND FRIDAY IN OUR CWA BUT STILL QUITE COLD. MUCH
LESS WARMING THAN PREVIOUSLY FORECAST FOR THIS WEEKEND...AND DAY
CREW HAS REMOVED ALL MENTION OF FREEZING RAIN AND/OR RAIN...WHICH
LOOKS CORRECT. PROGS SHOW A WEAK PACIFIC STORM COMING IN FROM OFF
CALIF FRIDAY NIGHT WITH PCPN SPREADING PCPN NEWD INTO OUR SRN ZONES
...ALL AS SNOW. THAT SYSTEM LOOKS TOO WEAK TO SCOUR OUT OUR COLD
AIR BUT ALSO TOO WEAK TO PRODUCE MUCH SNOW ACCUMULATION. THE
FOLLOWING PACIFIC STORM...FOR SATURDAY NIGHT AND SUNDAY...LOOKS
STRONGER WITH MORE SNOW AND CONTINUED SLOW WARMING...BUT THEN THE
FLOW ALOFT IS PROGGED TO TURN FROM WESTERLY TO NORTHWESTERLY AGAIN
SO NO FURTHER WARMING IS EXPECTED. COULD BE QUITE A BIT OF SNOW IN
OUR CWA BY LATE SUNDAY. UNTIL THEN CURRENT FORECAST LOOKS JUST
ABOUT RIGHT.
&&
.AVIATION...VFR WILL CONTINUE THROUGH THURSDAY UNDER MOSTLY CLEAR
SKIES. SURFACE WINDS WILL BE LIGHT. WINDS ALOFT WILL BE MODERATE
NORTHWEST.
&&
.PREV DISCUSSION...
SHORT TERM...TONIGHT THROUGH FRIDAY...BITTERLY COLD AIR MASS
CONTINUES OVER THE FORECAST AREA. ANOTHER NIGHT OF WELL BELOW ZERO
READINGS IS IN STORE FOR MUCH OF THE AREA...WHILE THE TREASURE
VALLEY IN SOUTHWEST IDAHO HOVERS WITHIN A COUPLE DEGREES OF
ZERO...PLUS OR MINUS. IF BOISE DROPS BELOW ZERO TONIGHT...IT WOULD
MARK THE THIRD CONSECUTIVE NIGHT OF BELOW ZERO READINGS. OVERNIGHT
TEMPERATURES LOOK SIMILAR IN MANY RESPECTS TO LAST NIGHT BUT MID AND
HIGH CLOUD TO OUR EAST MAY JUST BE ENOUGH TO HOLD MINS UP A FEW
DEGREES ON THE EASTERN FLANK OF THE AREA. WESTERN SECTIONS OF THE
AREA EXPECTED TO BE CLEAR. DESPITE CORE OF COLD AIR EAST OF THE
REGION...THE CENTER OF HIGH PRESSURE REMAINS DIRECTLY OVER THE
STATE. HAVE INCLUDED PATCHY FOG IN THE LOWER TREASURE VALLEY DURING
THE NEXT TWO NIGHTS BUT NOT ANTICIPATING WIDESPREAD FOG CONDITIONS
DUE TO THE VERY DRY COLD AIR MASS. AIR QUALITY IS EXPECTED TO WORSEN
TO SOME EXTENT TOMORROW AND FRIDAY WITH SHALLOW COLD AIR REMAINING
AND HIGH PRESSURE STAGNATING ...BUT NOT EXPECTING WIDESPREAD HAZE OR
FOG WITH INVERSION INDICES SHOWING ONLY A MODERATE INVERSION. A WEAK
SHORT WAVE APPROACHES THE WEST COAST FRIDAY PUSHING INCREASING
CLOUDS INTO EASTERN OREGON WITH A SLIGHT CHANCE OF SNOW OVER THE
STEEN MOUNTAINS AND THE OWYHEE RANGE LATE IN THE DAY. SYSTEM DOES
NOT APPEAR TO BE STRONG ENOUGH TO SCOUR OUT COLD AIR...THUS HAVE
KEPT COLD READINGS LOCKED IN FOR ANOTHER DAY WHICH IS LIKELY TO
LINGER INTO THE WEEKEND.
LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...HAVE MADE SIGNIFICANT
CHANGES TO WEEKEND FORECAST AS ONLY SLIGHT MODIFICATION OF CURRENT
AIRMASS IS EXPECTED. FORECAST AREA REMAINS IN CYCLONIC FLOW AROUND
COLD ARCTIC LOW IN SW CANADA WITH MILD/MOIST PACIFIC FLOW SETUP OVER
CENTRAL CA/NV. WHILE MODEL SOLUTIONS SHOW SIMILAR LARGE-SCALE
PATTERN/STORM TRACK HAVE GONE CLOSER TO THE NAM/DGEX MODEL SOLUTIONS
FOR TEMPS FOR SAT-MON WHICH SHOWS LESS MODIFICATION OF THE CURRENT
AIRMASS. FEEL THIS IS SUPPORTED BY SOUTHERN STORM TRACK AND WEAK
WARM-ADVECTION SIGNAL OVER THE FORECAST AREA AHEAD OF THE SYSTEM ON
SATURDAY. GFS SOLUTION HAS TRENDED COOLER WITH TEMPS...THOUGH FEEL
IT REMAINS TOO WARM FOR THE WEEKEND. WITH TEMPS WITHIN A COUPLE
DEGREES OF FREEZING IN LOWER VALLEYS EXPECT PRECIP TO BE ALL SNOW
FOR SAT/SUN. LIGHT SNOW FRIDAY NIGHT AND SATURDAY WITH WEAK
WARM-ADVECTION WILL AMOUNT TO AN INCH OR LESS EVEN IN THE MTNS. WILL
SEE GREATER AMOUNTS SATURDAY NIGHT AND SUNDAY AS UPPER LOW MOVES
THOUGH NORTHERN NV AND WEAK FEATURE MOVING AROUND ARCTIC LOW SLIDES
THROUGH THE PAC NW. ACTIVE PATTERN FOR NEXT WEEK WITH MODELS STILL
SHOWING GRADUAL MODERATION IN AIRMASS. HAVE STAYED WITH NEAR NORMAL
TEMPS AND ABOVE CLIMO. POPS.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.
&&
$$
WEATHER.GOV/BOISE
DISCUSSION...LC
AVIATION.....JT
PREV HORT TERM...GS
PREV LONG TERM....DG/DD
