National Weather Service Tucson Arizona
AREA FORECAST DISCUSSION
FXUS65 KTWC 092102 AFDTWC AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TUCSON AZ 202 PM MST TUE FEB 9 2010 .SYNOPSIS...ANOTHER WINTER STORM WILL BRING VALLEY RAIN AND MOUNTAIN SNOW BY LATE WEDNESDAY INTO THURSDAY. THIS NEXT STORM WILL BE COLDER THAN RECENT ONES...SO THE SNOW LEVEL WILL BE MUCH LOWER WEDNESDAY NIGHT AND EARLY THURSDAY WITH SIGNIFICANT ACCUMULATIONS POSSIBLE ABOVE 4000 FEET OR EVEN LOWER. DRY AND WARMER FRIDAY INTO THE WEEKEND UNDER HIGH PRESSURE. && .DISCUSSION...WATER VAPOR IMAGERY SHOWS THE STRONG LOW PRESSURE SYSTEM SPINNING JUST OFFSHORE OF CENTRAL CALIFORNIA WITH IR AND VISIBLE SATELLITE IMAGERY SHOWING PLENTY OF CLOUDINESS AHEAD OF THE LOW OVER CALIFORNIA...NEVADA AND DEVELOPING RAPIDLY ACROSS UTAH AND ARIZONA. MEANWHILE...A LARGE PLUME OF MOISTURE OVER THE SOUTHEASTERN PACIFIC IS STREAMING NORTHEAST ACROSS SRN BAJA AND INTO NORTHERN MEXICO. AS THE EVENING PROGRESSES...EXPECTING CLOUDINESS TO CONTINUE TO FILL IN ACROSS THE DESERT SOUTHWEST AS THE LOW MOVES SOUTH ALONG THE CALIFORNIA COAST TOWARD THE SAN DIEGO AREA BY EARLY WEDNESDAY MORNING. THE MODELS SHOW A BAND OF SHOWERS MAINLY ALONG THE EASTERN PERIPHERY OF THE LOW EARLY WEDNESDAY ALONG THE COLORADO RIVER BASIN. THE LOW IS PROGGED TO BE OVER SOUTHWESTERN ARIZONA OR NORTHWESTERN SONORA BY MID TO LATE AFTERNOON ON WEDNESDAY. AS A RESULT...EXPECT SHOWERS TO INCREASE FROM WEST TO EAST DURING THE DAY. FOR NOW THE MODELS SHOW A BIT OF DISAGREEMENT WITH REGARD TO QPF VALUES AND THUS SNOW AMOUNTS. HOWEVER...ALL OF THE MODELS ARE SHOWING A STRONG JET AT AROUND 200-300MB...GENERALLY GREATER THAN 150 KNOTS DEVELOPING ACROSS THE SE CORNER OF ARIZONA...THUS SRN PORTIONS OF ARIZONA WILL BE UNDER THE LEFT FRONT QUADRANT (LEFT EXIT REGION) OF THE JET...SO DYNAMICS WITH THIS SYSTEM LOOK QUITE GOOD. GFS MODEL CROSS-SECTIONS ARE SHOWING OMEGA VALUES OF 15 TO 20 MICROBARS PER SECOND BY LATE WEDNESDAY AFTERNOON OVER MAINLY CENTRAL PORTIONS OF THE FORECAST AREA. THESE VALUES SHIFT EAST DURING THE EVENING AND OVERNIGHT HOURS. I KEPT THE INHERITED QPF/SNOW AMOUNT FORECAST FROM THE NIGHT SHIFT. I ALSO INHERITED A WINTER STORM WATCH FOR ALL OF THE HIGHER ELEVATIONS OF SOUTHEAST ARIZONA FOR WEDNESDAY AFTERNOON THROUGH LATE THURSDAY MORNING. WITH SOME CONTINUED UNCERTAINTY WITH REGARD TO THE TIMING...POSITION AND STRENGTH OF THIS SYSTEM I DECIDED TO HOLD OFF ON ANY UPGRADES TO THE WATCH...SINCE TRYING TO FINE TUNE AREAS THAT MAY NEED A WARNING ARE STILL A BIT DIFFICULT AND ALL DEPEND ON THE TRACK OF THE STORM AS WELL AS HOW MUCH OF THE TROPICAL MOISTURE THE LOW IS ABLE TO TAP INTO AND PULL NORTHWARD INTO ARIZONA. AS THE LOW MOVES OVER SRN ARIZONA AND NORTHERN SONORA THE MODELS PROG THIS SYSTEM TO BE COLD WITH 500MB TEMPS OF AROUND -24 TO -26 DEGS CELSIUS. THEREFORE...I INCLUDED A MENTION OF A SLIGHT CHANCE OF THUNDERSTORMS TO ACCOMPANY THE SHOWERS...MAINLY FOR WEDNESDAY AFTERNOON AND THROUGHOUT THE OVERNIGHT HOURS. SNOW LEVELS ARE EXPECTED TO BE RATHER LOW WITH SNOW LEVELS GENERALLY AROUND 3500-4500 FEET DURING THE OVERNIGHT HOURS WEDNESDAY NIGHT INTO THURSDAY. THIS COULD ALSO CHANGE DEPENDING ON WHAT SUBSEQUENT MODEL RUNS HAVE TO SHOW WITH REGARD TO SNOW LEVELS. THE LOW SHOULD QUICKLY KICK TO THE EAST THURSDAY WITH PRECIPITATION CHANCES DECREASING CONSIDERABLY DURING THE DAY. FOR THE REMAINDER OF FORECAST PERIOD EXPECTING RIDGING TO GENERALLY INFLUENCE THE WEATHER ACROSS THE DESERT SOUTHWEST WITH SOME SYSTEMS DROPPING OVER THE TOP OF THE RIDGE AND PERHAPS CLIPPING THE EASTERN SECTIONS OF THE FORECAST AREA FROM TIME TO TIME. HOWEVER...FOR NOW I KEPT A DRY FORECAST GOING. && .AVIATION...INCREASING HIGH CLOUDS FROM THE SOUTHWEST TODAY. SURFACE WINDS ARE EXPECTED TO BE LESS THAN 15 KTS AND ADHERE TO TYPICAL DIURNAL PATTERNS. HIGH PRESSURE WILL GIVE WAY TO A STRONG STORM MOVING IN FROM THE WEST BY LATE WEDNESDAY WITH LOWERING CEILINGS AND INCREASING CHANCES FOR PRECIPITATION THROUGH THE DAY ON WEDNESDAY. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS. && .FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME. && .TWC WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM 3 PM MST WEDNESDAY THROUGH 11 AM MST THURSDAY ABOVE 4000 FEET FOR AZZ019-029-030-032>035.
MOLLERE WEATHER.GOV/TUCSON
|
|
|
Webmaster
US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Tucson Weather Forecast Office
520 North Park Ave, Suite 304
Tucson, AZ 85719
Tel: (520) 670-6526
|
Disclaimer
Information Quality
Credits
Glossary |
Privacy Policy
Freedom of Information Act
About Us
Career Opportunities
|