Hard Freeze Warning 1, NWS Denver/Boulder, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
345 PM MDT THU OCT 4 2012

.SHORT TERM...AREA OF STRATUS STILL LINGERING ALONG FOOTHILLS OF
BOULDER AND JEFFERSON COUNTIES...SHOWING SIGNS OF DISSIPATING.
OTHERWESE...MID LEVEL MOISTURE MOVING ACROSS AREA BEING ADVECTED
IN FROM THE DESERT SOUTHWEST. BATCH OF CUMULUS HAD FORMED ACROSS
SOUTHERN MOUNTAINS ABOVE THE STABLE LAYER. AIRMASS SLIGHTLY
UNSTABLE IN THIS AREA WITH RADAR SHOWING A FEW LIGHT SHOWERS
ACROSS SOUTHERN PARK COUNTY. MODELS KEEP SOME LOW CAPE OVER
MOUNTAINS AND PARK COUNTY INTO THE EVENING HOURS...AND WILL
CONTINUE WITH THE SLIGHT CHANCE OF SHOWERS. SOME SNOW IS POSSIBLE
OVER THE HIGHER AREAS WITH MINIMAL ACCUMULATION. ACROSS
PLAINS...NOT EXPECTING STRATUS TO REDEVELOP AS MID AND HIGH LEVEL
CLOUDS SPREAD ACROSS AREA. LOOKING LIKE TEMPERATURES ACROSS PLAINS
WILL AGAIN DROP INTO THE LOWER AND MIDDLE 30S OVERNIGHT ALONG
WITH SOME UPPER 20S IN LOW LYING AREAS. DECIDED TO HOIST FROST
ADVISORY FOR ALL OF THE PLAINS AS ONLY A FEW AREAS THIS MORNING
WERE BELOW FREEZING. ON FRIDAY....UPPER TROUGH TO CONTINUE TO DIG
ACROSS GREAT BASIN WITH FLOW ALOFT BECOMING WESTERLY. BROAD
SURFACE HIGH ACROSS CENTRAL PLAINS TO KEEP UPSLOPE FLOW GOING
ACROSS PLAINS. UPPER LEVEL JET WILL BEGIN TO MOVE SOUTH ACROSS
WYOMING DURING THE DAY WITH NORTHEASTERN COLORADO IN THE FAVORED
LEFT EXIT REGION BY MID DAY. THIS TO PROVIDE LIFT FOR THE
DEVELOPMENT OF SOME SHOWERS OVER NORTHEAST CORNER. AS JET SAGS
SOUTHWARD ACROSS WYOMING...PRECIP CHANCES TO SPREAD SOUTH ACROSS
PLAINS DURING THE AFTERNOON WITH THE BEST CHANCE ALONG THE
NORTHERN BORDER. TEMPERATURES LOOK TO BE COLD ENOUGH FOR SNOW
ALONG CHEYENNE RIDGE WITH EITHER SNOW OR A MIX OF RAIN AND SNOW
ACROSS THE NORTHEAST CORNER. ANY ACCUMULATIONS WILL BE LIGHT.
CLOSER TO DENVER AND ALONG NORTHERN FOOTHILLS...PRECIP SHOULD BE
RAIN THROUGH THE AFTERNOON.

.LONG TERM...UPPER JET ALOFT WILL BE SINKING SOUTH OVER THE AREA
FRIDAY NIGHT WITH THE UPPER TROUGH DROPPING FROM MONTANA INTO
WYOMING. HIGH SURFACE PRESSURE CENTER WILL BE MOVING FROM
SASKATCHEWAN SOUTH TO SOUTH DAKOTA AS WELL KEEPING UPSLOPE IN
PLACE. QG VERTICAL VELOCITIES WILL BE INCREASING UPWARD AS THE
UPPER TROUGH NEARS PROVIDING DYNAMICS FOR A CHANCE OF RAIN MIXING
WITH SNOW IN THE EVENING...THEN SNOW LIKELY AFTER MIDNIGHT OVER
THE NORTHEASTERN PLAINS. THE 700 MB FLOW MAY PLAY WITH THE AMOUNT
OF PRECIPITATION AROUND THE URBAN CORRIDOR AS THE SOUTHERLY TO SOUTHWESTERLY
FLOW COULD TEND TO DOWNSLOPE. HOWEVER WITH THE QG LIFT AND THE
UPSLOPE AT LOWER LEVELS WILL KEEP AT LEAST A SLIGHT CHANCE.
THE MOUNTAINS MAY SEE A FEW SHOWERS WEST OF THE DIVIDE IN THE
EVENING THEN DRY OUT AS THE FRONTAL AIRMASS WILL REMAIN EAST OF
THE DIVIDE. THE FOOTHILLS WILL LIKELY SEE SOME LIGHT SNOW...BUT
THE BEST DYNAMICS WILL REMAIN OVER THE EASTERN PLAINS. TEMPERATURES
FRIDAY NIGHT WILL BE IN THE UPPER 20S TO NEAR 30...PROMPTING THE
FREEZE WATCH FOR THE PLAINS.

ON SATURDAY...THE SURFACE HIGH PUSHES FURTHER SOUTH OVER THE FAR
NORTHEASTER CORNER OF THE STATE AND THE UPPER TOUGH WILL STRETCH
SOUTHWEST DOWN INTO NORTHEASTERN COLORADO. THIS WILL GIVE THE BEST
CHANCE FOR SNOW DURING THE MORNING FOR THE PLAINS BEFORE THE
SYSTEM CONTINUES PUSHING SOUTH. THE FRONT RANGE MOUNTAINS AND
FOOTHILLS MAY SEE A FEW AREAS OF SNOW...THEN WILL BE QUICKLY
CLEARING OUT AS DRY WESTERLY FLOW MOVES IN BEHIND THE DEPARTING
SYSTEM. AREAS WEST OF THE DIVIDE WILL LIKELY STAY DRY SATURDAY. THE
EXTRA PUSH AND UPPER TROUGH WILL SPREAD THE COLDEST TEMPERATURES
OVER THAT THE STATE WILL SEE WITH THIS SYSTEM. HIGHS ARE NOT
EXPECTED TO GET MUCH HIGHER THAN THE LOW 40S ACROSS THE ENTIRE
FORECAST AREA. SATURDAY NIGHT AS THE SYSTEM CONTINUES SOUTH AND
PRECIPITATION AND SKIES CLEAR...TEMPERATURES WILL DROP INTO THE
MID 20S OR LOWER. WILL LIKELY NEED A HARD FREEZE HEADLINE FOR THE
PLAINS THIS NIGHT.

SUNDAY AND MONDAY WILL BE A WARMING AND DRYING TREND WITH
TEMPERATURES BUMPING BACK UP INTO THE 50S AND 60S AS A RIDGE
BUILDS ALOFT. THEN ANOTHER SHORTWAVE TROUGH FROM THE NORTH WILL
PUSH A WEAK FRONT THROUGH THE AREA....DROPPING TEMPERATURES ONLY A
FEW DEGREES. A RIDGE WILL BUILD YET AGAIN AS A CUTOFF LOW SPINS
OVER CALIFORNIA THROUGH THURSDAY BRINGING SEASONAL TEMPERATURES
AND MOSTLY DRY WEATHER. MODELS ARE HINTING AT THE CUTOFF LOW
GETTING CAUGHT IN THE FLOW TO MOVE TOWARD THE STATE FRIDAY.

&&

.AVIATION...WEAK EASTERLY WINDS TO PERSIST THROUGH THE OVERNIGHT
HOURS...BECOMING NORTHEAST AS SURFACE HIGH MOVES INTO THE NORTHERN
PLAINS. MID AND HIGH LEVEL CLOUDS TO CONTINUE TO INCREASE DURING
THE EVENING. NOT EXPECTING STRATUS TO REDEVELOP DUE TO INCREASE IN
MID LEVEL CLOUDS. CEILINGS OF 6000 FEET AGL POSSIBLE AROUND 18Z
WITH A SLIGHT CHANCE OF RAIN SHOWERS BY 21Z...MAINLY NORTH AND
EAST OF DENVER. FOR NOW WILL CONTINUE WITH VCSH. ANY SHOWERS THAT
DEVELOP SHOULD BE RAIN THROUGH 00Z...THOUGH SOME SNOW COULD BE
MIXED WITH THE RAIN DURING THE EVENING. BETTER CHANCE FOR SNOW
AFTER MIDNIGHT FRIDAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY FROM MIDNIGHT TONIGHT THROUGH 9AM MDT FRIDAY
MORNING FOR ALL OF THE PLAINS..COZ038>051.
FREEZE WATCH FROM MIDNIGHT FRIDAY THROUGH 10 AM SATURDAY FOR
ALL OF THE PLAINS...COZ038>051.

&&

SHORT TERM...D-L
LONG TERM....KRIEDERMAN
AVIATION...D-L