High Wind in Colorado, October 18 to 19, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
420 AM MDT THU OCT 18 2007

.SHORT TERM...PRESSURE GRADIENTS ACROSS COLORADO THIS MORNING ARE
COMBINING WITH MODERATE NORTHWESTERLY FLOW ALOFT TO PRODUCE GUSTY
WINDS ALONG THE FRONT RANGE AND OUT ONTO THE PLAINS.  BREEZY
CONDITIONS ARE EXPECTED TO PERSIST THROUGH MUCH OF THE DAY ACROSS
THE PLAINS AS THE CIRCULATION AROUND A LARGE LOW PRESSURE AREA OVER
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY CONTINUES.  THE
PRESSURE GRADIENTS ACROSS THE STATE...ALTHOUGH ABOUT 16 MBS FOR
KGJT-KGLD...ARE NOT AS STRONG AS THEY WERE FORECAST BY PREVIOUS
MODEL RUNS.  THUS IT SEEMS THAT PEAK WINDS ON THE PLAINS WILL ONLY
BE IN THE 30S WITH GUSTS INTO THE 40S...BELOW HIGH WIND CRITERIA.
BUFR SOUNDINGS ON THE PLAINS ONLY SHOW A PEAK WIND OF 44 KTS IN THE
MIXED LAYER THIS AFTERNOON.  WILL THEREFORE CANCEL THE HIGH WIND
WATCH ON THE NORTHEAST PLAINS.  IN ADDITION TO THE WIND ON THE
PLAINS...SOME SNOW HAS BEEN FALLING OVER THE HIGHER MOUNTAIN PEAKS
THIS MORNING.  THIS SCATTERED ACTIVITY SHOULD CONTINUE THROUGH THE
MORNING AND THEN DECREASE THROUGH THE AFTERNOON AS SUBISDENCE FROM A
BUILDING UPPER RIDGE SPREADS OVER THE STATE FROM THE SOUTHWEST.

FOR LATER TONIGHT...CONTINUING NORTHWESTERLY FLOW IS GOING TO SET UP
A PERIOD OF CHINOOK WINDS ALONG THE FRONT RANGE.  CROSS SECTIONS
ACROSS THE STATE SHOW AN AMPLIFIED WAVE DEVELOPING OVER THE
FOOTHILLS BY 03Z THIS EVENING AND THEN CONTINUING THROUGH THE
NIGHT.  FURTHER ALOFT...A 110 KNOT JET WILL BE IN PLACE OVER WESTERN
WYOMING AND NORTHWEST COLORADO WITH THE FOOTHILLS LOCATED UNDER THE
NOSE OF THE APPROACHING JET.  AS A STABLE LAYER AT MOUNTAIN TOPS
FORMS IN THE EVENING...THE VERTICAL SHEAR PROFILE WILL BECOME
FAVORABLE FOR THE CHINOOK WIND EVENT.  FOR THESE REASONS...WILL
ISSUE A NEW HIGH WIND WATCH FOR THE FOOTHILLS AND ADJACENT PLAINS
FROM 03Z TONIGHT THROUGH 18Z ON FRIDAY.  ADDITIONAL DISCUSSION OF
THIS SITUATION FOLLOWS.  OTHER THAN THE WINDS...THE REST OF THE
WEATHER SHOULD BE DRY WITH TEMPERATURES NEAR TO SLIGHTLY BELOW
NORMAL.

.LONG TERM...SHORT RANGE MODELS SHOWING A CLASSIC CHINOOK SETUP
CONTINUING INTO FRIDAY MORNING.  STRONG UPPER LEVEL JET SHIFTS NORTH
OF THE AREA LATE TONIGHT INTO FRIDAY MORNING WITH LARGE SCALE
SUBSIDENCE...STRENGTHENING MOUNTAIN TOP STABLE LAYER...AND
DECREASING VERTICAL SPEED SHEAR.  THE ONLY DRAWBACK FOR A FRONT
RANGE WIND EVENT WOULD BE THE ACTUAL STRENGTH OF THE CROSS MOUNTAIN
FLOW...WHICH UPSTREAM OF THE MOUNTAINS IS ABOUT 40 KNOTS.  THAT
WOULD BE MARGINAL FOR HIGH WINDS BUT THE QUALITY OF THE OTHER
FACTORS STILL SUPPORT A HIGHLIGHT AND POTENTIAL FOR 80 MPH WIND
GUSTS IN FAVORED CHINOOK AREAS.  DONT SEE STRONGER GUSTS GETTING
EAST OF I-25 IN THIS SCENARIO.

NEXT FEATURE TO FOCUS ON WILL BE THE TROUGH THAT WILL MOVE ACROSS
COLORADO THIS WEEKEND.  WHILE THE GFS AND NAM ARE MORE PROGRESSIVE...
THE 00Z ECMWF HELD STRONG WITH ITS DEEPER SOLUTION.  THERE IS A
CONSIDERABLE AMOUNT OF JET ENERGY STREAMING ACROSS THE PACIFIC SO
OBVIOUSLY CANT RULE OUT A STRONGER TROUGH.  EVEN SOME OF THE GFS
ENSEMBLES HAD THIS SYSTEM CARVING OUT A DEEPER TROUGH.  NO MATTER
WHAT THE DEPTH...THIS TROUGH SEEMS TO BE CARRYING THE COLDEST AIR OF
THE SEASON AND THERE WOULD BE A PERIOD OF CONSIDERABLE Q-G VERTICAL
MOTION.  FOR THIS REASON WILL GO WITH A CHANCE OF RAIN...AND
YES...ADD THE SNOW WORD FOR THE LOWER ELEVATIONS INCLUDING DENVER
LATE SATURDAY NIGHT INTO SUNDAY.

AFTER THIS SYSTEM...THE WEATHER PATTERN SEEMS TO SETTLE DOWN A BIT
WITH RIDGING AND WARMING BY THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...SHOULD SEE NO PROBLEMS WITH CIGS AND VSBYS THROUGH TODAY
AND TONIGHT.  HOWEVER...BREEZY WEST TO NORTHWEST WINDS THROUGH THIS
MORNING MAY CAUSE CROSSWIND PROBLEMS.  WIND SPEEDS WILL INCREASE BY
MID-MORNING AS DAYTIME HEATING DISSIPATES LOW LEVEL INVERSIONS AND
WINDS ALOFT BEGIN MIXING TO THE SURFACE.  WINDS SHOULD PEAK BETWEEN
18Z AND 21Z THEN BEGIN DIMINISHING.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...HIGH WIND WATCH FOR THE FRONT
  RANGE FOOTHILLS AND ADJACENT PLAINS LATE THIS EVENING TIL NOON
  FRIDAY...ZONES 35..36..38..AND 39.

&&

KDRBY/BARJENBRUCH

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