FXUS65 KVEF 022336
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
335 PM PST WED DEC 2 2009

.SYNOPSIS...HIGH PRESSURE WILL KEEP DRY WEATHER IN PLACE BUT COLD 
AIR AND LOCALLY GUSTY NORTH WINDS WILL USHER IN SUBFREEZING 
TEMPERATURES TO MUCH OF THE MOJAVE DESERT THURSDAY NIGHT AND FRIDAY 
NIGHT. THE HIGH PRESSURE RIDGE WILL BREAK DOWN GOING INTO THE 
WEEKEND...LEADING TO A SIGNIFICANT PATTERN CHANGE WITH A SERIES OF 
STRONG PACIFIC STORMS IMPACTING THE REGION LATE IN THE WEEKEND 
THROUGH NEXT WEEK.
&&

.SHORT TERM...THE BROAD COLD CANADIAN AIR MASS COULD BE SEEN ON 
SATELLITE IMAGERY DROPPING OUT OF SOUTHERN CANADA INTO THE 
INTERMOUNTAIN WEST AND THE PLAINS THIS AFTERNOON. THE LATEST MODEL 
GUIDANCE CONTINUES TO SHOW THE WEST EDGE OF THIS AIR MASS SPILLING 
INTO THE MOJAVE DESERT AIDED BY MODERATE NORTHEAST WINDS DEVELOPING 
TONIGHT AND THURSDAY. THE MAIN IMPACT WILL BE SUBFREEZING LOW 
TEMPERATURES THURSDAY NIGHT AND FRIDAY NIGHT ACROSS THE MOJAVE 
DESERT...PARTICULARLY THE LAS VEGAS VALLEY. NORTH BREEZES THURSDAY 
NIGHT SHOULD KEEP THE BOUNDARY LAYER SOMEWHAT MIXED AND THUS LOW 
TEMPERATURES WILL BE MODERATED SLIGHTLY. ONE THING WORKING AGAINST 
MAXIMUM COOLING FRIDAY NIGHT IS A BLANKET OF CIRRUS WHICH IS 
FORECAST TO SPREAD OVER SOUTHERN NEVADA MUCH OF FRIDAY NIGHT. 
HOWEVER...IF THIS CIRRUS SHIELD LARGELY PUSHES SOUTHEAST SHORTLY 
AFTER MIDNIGHT...MAXIMUM RADIATIONAL COOLING WILL OCCUR SINCE WINDS 
WILL BE LIGHT. THIS WILL BE THE FIRST NIGHT WITH WIDESPREAD 
SUBFREEZING TEMPERATURES THIS SEASON. A SPECIAL WEATHER STATEMENT 
WAS ISSUED TO RAISE AWARENESS GIVEN THE EXTENDED PERIOD OF MILD 
WEATHER WE HAVE EXPERIENCED. THE PATTERN TRANSITIONS SATURDAY AS THE 
RIDGE BREAKS DOWN AND A LOW PRESSURE SYSTEM DIVES OUT OF THE PACIFIC 
NORTHWEST INTO THE GREAT BASIN. THIS WILL BRING WARMER SOUTHWEST 
FLOW ACROSS THE REGION SATURDAY BEFORE THE WEATHER GETS INTERESTING 
EARLY NEXT WEEK. SEE DETAILS BELOW.

.LONG TERM...MODELS ARE IN DECENT AGREEMENT IN SHOWING A SIGNIFICANT 
CHANGE TO THE WEATHER PATTERN BY THE END OF THE WEEKEND AND NEXT 
WEEK. UPPER LOW...WITH HAS BEEN ADVERTISED BY THE MODELS...WILL DROP 
SOUTH INTO THE PACIFIC NORTHWEST SUNDAY AND GRADUALLY MOVE SOUTH 
TOWARD FAR NORTHERN CALIFORNIA. THE MAIN DIFFERENCES BETWEEN THE GFS 
AND THE ECMWF IS HOW FAR WEST THE LOW MOVES. THE GFS KEEPS THE LOW 
ONSHORE SUNDAY AND MONDAY BEFORE PUSHING IT EAST INTO NORTHERN 
NEVADA. THE ECMWF DROPS THE LOW FURTHER TO THE SOUTHWEST BEFORE 
QUICKLY SHIFTING IT OFF TO THE EAST AHEAD OF A STRENGTHENING EASTERN 
PACIFIC RIDGE. BOTH MODELS ARE SHOWING MOISTURE BEING TAPPED INTO 
THE LOW WITH HIGH AMOUNTS OF QPF PUSHING INTO NORTHERN AND CENTRAL 
CALIFORNIA. THE FLOW IS FORECAST TO REMAIN NEARLY ZONAL OVER THE CWA 
MONDAY AND TUESDAY WHICH WILL KEEP THE MAJORITY OF THE PRECIPITATION 
OVER THE UPPER ELEVATIONS OF THE SIERRA WITH A DECENT AMOUNT OF 
RAINSHADOWING EASTWARD. DUE TO THE COMPLEXITY AND STRENGTH OF THIS 
SYSTEM WILL KEEP CHANCE POPS OVER MUCH OF THE CWA MONDAY AND TUESDAY 
WITH THE BEST CHANCES LOOKING TO REMAIN OVER THE NORTHERN CWA. 
PLENTY OF COLD AIR BEHIND THIS SYSTEM AND TEMPERATURES ARE EXPECTED 
TO REMAIN BELOW NORMAL THROUGH THE PERIOD. ANOTHER SYSTEM PUSHING 
INTO THE PACIFIC NORTHWEST THURSDAY AND FRIDAY LOOKS TO BE WETTER 
SINCE THE MAIN TRAJECTORY IS DIRECTLY FROM THE PACIFIC AND THIS 
SYSTEM LOOKS TO HAVE A BETTER CHANCE OF BRING RAIN TO MUCH OF THE 
CWA. 
&&

.AVIATION...FOR MCCARRAN...LIGHT WINDS UNDER 6 KNOTS EXPECTED TO 
CONTINUE THROUGH TONIGHT AND EARLY THURSDAY. A TIGHTENING SURFACE 
PRESSURE GRADIENT WILL ALLOW WINDS TO INCREASE AFTER 17Z THURSDAY 
FROM THE NORTHEAST AROUND 7-10 KNOTS. THESE WINDS ARE EXPECTED TO 
CONTINUE THROUGH THURSDAY AFTERNOON. NO SIGNIFICANT CLOUDS ARE 
EXPECTED.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...WINDS WILL REMAIN RELATIVELY LIGHT OVER THE AREA 
THROUGH THURSDAY MORNING FOLLOWING LOCAL DIURNAL PATTERNS. GUSTIER 
NORTH WINDS WILL DEVELOP THURSDAY AFTERNOON...PRIMARILY DOWN THE 
COLORADO RIVER VALLEY...IMPACTING LOCATIONS LIKE LAUGHLIN AND 
NEEDLES. WIND GUSTS TO 25 MPH SHOULD BE ANTICIPATED IN THOSE 
LOCATIONS ON THURSDAY AFTERNOON. NO SIGNIFICANT CLOUDS ARE EXPECTED.
&&

.FIRE WEATHER...LOCALLY GUSTY NORTH WINDS...ESPECIALLY DOWN THE 
COLORADO RIVER VALLEY...WILL USHER IN A VERY DRY AIRMASS ON 
THURSDAY. MINIMUM RELATIVE HUMIDITY VALUES WILL DROP INTO THE LOW 
TEENS AND SINGLE DIGITS THURSDAY AND FRIDAY. HOWEVER...WIND GUSTS 
ARE EXPECTED TO GENERALLY REMAIN BELOW 30 MPH.
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
AZ...NONE.
CA...NONE.
&&

$$

ADAIR/GORELOW

HTTP://WEATHER.GOV/LASVEGAS