000
FXUS63 KDMX 201136 AAA
AFDDMX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
536 AM CST THU NOV 20 2008
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
STRATUS CONTINUES TO OVERCAST THE AREA BEHIND YESTERDAYS COLD
FRONT...AND LOOKS TO CONTINUE THROUGH MOST OF TODAY. A SHORTWAVE
MOVING QUICKLY THROUGH NORTHWESTERLY FLOW ALOFT WILL PUSH A WEAK
REINFORCING SHOT OF COLDER SURFACE AIR THROUGH THE STATE. WEAK LIFT
ASSOCIATED WITH THIS SHORTWAVE AND HIGH RH NEAR THE LOW-LEVEL
INVERSION AS INDICATED BY FORECAST SOUNDINGS ARE SUPPORTIVE OF
SCATTERED FLURRIES THIS MORNING...EXCEPT IN THE SOUTHWEST WHERE LIFT
WILL BE WEAKER...RH LOWER...AND SATELLITE IMAGERY INDICATES POSSIBLE
BREAKING UP OF THE STRATUS DECK. SFC OBS ALREADY SHOW FLURRIES IN ND
MOVING THIS WAY. HOWEVER...FORECAST SOUNDINGS ALSO INDICATE
SIGNIFICANT LOW-LEVEL DRYING WITH MIXING DURING THE AFTERNOON SO
HAVE REMOVED MENTION OF FLURRIES AFTER 18Z. OTHERWISE FEW CHANGES
MADE TO TODAYS FORECAST...IT WILL BE COLD AND BLUSTERY ACROSS THE
AREA.
LITTLE OF CONCERN OUTSIDE OF TEMPS TONIGHT AND INTO MUCH OF FRIDAY
AS SURFACE HIGH SETTLES INTO MO VALLEY REACHING MS RIVER BY LATE
AFTERNOON. HAVE GONE JUST ABOVE GUIDANCE TONIGHT AS...ALTHOUGH NOT
AS EMPHATIC...FORECAST SOUNDING CONTINUE TO SHOW MIXING THROUGH MUCH
OF THE NIGHT KEEPING TEMPS UP SOMEWHAT. ONLY EXCEPTION WAS FAR
WESTERN SITES...ESPECIALLY IN THE NISH VALLEY. INTO FRI HAVE
CONTINUED TO GO TOWARD LOW END OF GUIDANCE BASED ON FORECAST
SOUNDINGS WHICH ARE IN GOOD AGREEMENT. MOS LIKELY BEING TUGGED
UPWARD BY CLIMO WITH UNSEASONALLY COLD AIRMASS IN PLACE.
GFS/ECMWF REMAIN FAVORED MODELS WITH LATE FRI/SAT SYSTEM AND REMAIN
SIMILAR TO WHAT WAS DEPICTED LAST NIGHT. MID LEVEL THERMODYNAMIC
AND KINEMATIC FORCING SWEEPS THROUGH IA WITH WEAK STATIC STABILITIES
ON SWRN FLANK. UVM IN H7/H6 DENDRITIC LAYER...OR 290-295K...IS
QUITE STRONG AND SATURATED AND WILL RESULT IN PLENTY OF SNOWFALL
PRODUCTION ALOFT. ONLY DRAWBACK IS OVERCOMING DRY AIR IN LOWEST 1KM
WHICH WILL TAKE AWHILE AND PROBABLY NOT OCCUR UNTIL FORCING WANES
SOMEWHAT. PHASING OF DENDRITIC UVM AND ADEQUATE LOW LEVEL MOISTURE
SEEMS TO OCCUR NEAR FSD/SPW SHORTLY AFTER 00Z...PROGRESSING ACROSS
NRN IA TO EBS/IFA/MIW AREA TOWARD DAYBREAK. THIS DRY LOW LEVEL AIR
WILL LIKELY KEEP QPF AMOUNTS FAIRLY LOW. RECENT GFS COBB RATIOS
HAVE BEEN 10-13:1 AND STAYING IN THAT LINE SUGGESTS SNOWS FROM A
DUSTING TO AROUND AN INCH WITH PCPN LINGERING INTO SAT MORNING
BEFORE ENDING. WOULD NOT BE SURPRISED TO SEE VERY ISOLATED HIGHER
AMOUNTS IF SATURATION OCCURS SOONER CONSIDERING STRENGTH OF UVM AND
POTENTIAL INSTABILITY...BUT CONFIDENCE NOT ENOUGH TO PUT IN GENERAL
FORECAST. STILL CURIOUS THAT MOS POPS HAVE NOT RESPONDED MORE...BUT
HAVE CONTINUED TO GO HIGH END CHANCES AND LOW LIKELIES IN FAVORED
AREAS.
WARM ADVECTION AND INCREASING CLOUDS LOOK TO KEEP TEMPS NEARLY
STEADY FRI NIGHT...WITH MINS TOWARD HIGH END OF GUIDANCE. CLIMO MAY
AGAIN BE TUGGING AT MOS SAT VS SOUNDINGS SO HAVE AGAIN GONE TOWARD
LOW END WITH LITTLE CHANGE FROM PREVIOUS FORECAST SAT NIGHT. EARLY
NEXT WEEK BASICALLY UNCHANGED WITH CLOSED LOW AND ASSOCIATED FORCING
STAYING TO OUR NORTH. COULD SEE SOME LIGHT SNOW SHOWERS/FLURRIES AS
WEAK SHORT WAVES TRAVERSE DEEP CYCLONIC FLOW SUN NIGHT AND MON...BUT
THAT IS ABOUT IT. REMAINDER OF FORECAST DRY AS RIDGING CROSSES
CENTRAL CONUS MIDWEEK.
&&
.AVIATION...20/12Z
BIGGEST AVIATION IMPACT TODAY WILL BE LINGERING STRATUS THIS
MORNING...PRODUCING PREVAILING MVFR CIGS AT MOST TERMINALS. CIGS
SHOULD GRADUALLY LIFT THROUGH THE MORNING AS ATMOSPHERIC MIXING
RAISES THE INVERSION LEVEL...RESULTING IN CIG BASES AROUND FL035-040
BY MID TO LATE MORNING. CLOUDS WILL THEN GRADUALLY BREAK UP AND
CLEAR OUT DURING THE AFTERNOON...RESULTING IN CLEAR SKIES TONIGHT.
WINDS WILL PICK UP ONCE AGAIN AFTER SUNRISE THIS MORNING...THEN
TAPER OFF TOWARD SUNSET AND BECOME LIGHT BY EARLY MORNING FRIDAY AS
HIGH PRESSURE APPROACHES FROM THE WEST AND NORTH. THERE IS A
POSSIBILITY OF INTERMITTENT FLURRIES OR LIGHT SNOW SHOWERS THIS
MORNING...MAINLY AT THE NORTHERN SITES...HOWEVER THE RELATIVELY LOW
PROBABILITY OF OCCURRENCE AT A GIVEN TERMINAL AS WELL AS EXPECTED
SHORT DURATION PRECLUDES MENTION IN TAFS ATTM.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
JLW/BSS/REV
