000
FXUS65 KBOU 181058
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
458 AM MDT SAT MAY 18 2013

.SHORT TERM...UPPER TROUGH SLOWLY MOVING INTO THE ROCKIES TODAY
WITH SOUTHERLY FLOW ALOFT AHEAD OF IT. WELL ESTABLISHED SURFACE
TROUGH FROM THE BLACK HILLS TO THE TEXAS PANHANDLE. HIGH LEVEL
MOISTURE WILL INCREASE OVER EASTERN COLORADO BUT LOW/MID LEVELS
REMAINING QUITE DRY. EXCEPTION IS EAST OF THE SURFACE TROUGH WHERE
DEW POINTS ARE IN THE 60S. WITH THE SOUTHERLY FLOW ALOFT...NOT
MUCH MOTION EXPECTED TO THIS BOUNDARY AS THE TROUGH APPROACHES.
CURRENTLY A LITTLE EASTWARD MOTION WITH NIGHTTIME DRAINAGE WINDS
FURTHER WEST...BUT DIURNAL TRENDS AND PRESSURE FALLS TO THE SOUTH
MAY LEAD TO SOME EAST WINDS PUSHING SHALLOW MOISTURE WESTWARD INTO
NORTHEAST COLORADO DURING THE DAY. WITH THE DRY AIR ALOFT...I
SUSPECT THE AREAS BEHIND THE TROUGH AND AREAS THAT GET THE SHALLOW
MOISTURE ADVECTION WILL PROBABLY SEE THE MOISTURE MIX OUT THIS
AFTERNOON...LEAVING A SHARP BOUNDARY WITH BETTER MOISTURE NEAR THE
EASTERN BORDER POSSIBLY ARCING BACK INTO SEDGWICK AND PHILLIPS
COUNTIES. WITH THE CLOUD COVER RESTRAINING TEMPERATURES A
LITTLE...EXPECT WEAK CONVECTION BEHIND THE TROUGH WITH CAPES OF
500-1000 J/KG. IN THE BETTER MOISTURE CAPES WILL BE MORE LIKE
2000-3000 J/KG. EXPECT STERLING AND AKRON TO BE IN THE GRADIENT
WITH THE BETTER MOISTURE AROUND JULESBURG AND HOLYOKE.

THE SHEAR PROFILE IS NOT OPTIMAL FOR ROTATION AND TORNADOES...BUT
CERTAINLY ADEQUATE. TURNING IS MAINLY RIGHT AT THE SURFACE THEN
PRETTY LINEAR SHEAR AND NOT TERRIBLY STRONG...SURFACE WINDS WILL
BE FAIRLY LIGHT...BUT AGAIN ADEQUATE TO SUPPORT ORGANIZED TILTED
UPDRAFTS. SHEAR AND SUPERCELL THREAT MAY BE ENHANCED IN AN AREA OF
EAST TO NORTHEAST SURFACE WINDS IF THEY ARE ABLE TO BACK AROUND
THAT FAR AS PRESSURES FALL TO THE SOUTH...THIS WOULD LIKELY BE IN
AREAS NORTH AND NORTHEAST OF AKRON IN THE MID TO LATE AFTERNOON
HOURS. THERE MAY BE A BETTER BALANCE BETWEEN THE CAPE AND SHEAR AT
THIS TIME. FURTHER EAST THE VERY STRONG BOUYANCY MAY DOMINATE AND
MAKE IT HARDER TO HOLD INDIVIDUAL CELLS TOGETHER. PARAMETERS WILL
IMPROVE AGAIN THIS EVENING FURTHER EAST BUT THIS WILL PROBABLY BE
EAST OF COLORADO. WORTH NOTING THAT THE BOUYANCY FORECASTED FOR
THE NORTHEAST CORNER IS ABOVE WHAT WE NORMALLY SEE...3000 J/KG AND
THE SEVERE PARAMETERS SUCH AS SWEAT INDEX OF 300-450...TOTAL
TOTALS OVER 60...AND MOS SEVERE PROBABILITIES OVER 40 PERCENT ARE
ABOUT AS HIGH AS I HAVE SEEN IN OUR AREA. WITH THE
INSTABILITY...LIMITED SHEAR...AND RELATIVELY LOW FREEZING LEVELS
VERY LARGE HAIL IS PROBABLY THE MAIN THREAT...BUT ANYTHING IS
POSSIBLE. WEST OF FORT MORGAN STORMS SHOULD BE WEAK AND DRY
THOUGH SOME GUSTY WINDS POSSIBLE.

SOME COLD ADVECTION ALOFT BEHIND THE TROUGH...NORTHWEST WINDS
DEVELOPING LATE IN THE DAY PROBABLY WITH THE HELP OF SOME MOUNTAIN
CONVECTION. DIURNAL SHOWERS SHOULD DIMINISH OVER MOST OF THE AREA
EARLY...BUT THERE IS SOME MOISTURE MOVING INTO THE MOUNTAINS SO
SOME LOW POPS OVERNIGHT IN THE HIGH COUNTRY ARE STILL
APPROPRIATE...COLD ENOUGH FOR SNOW IN THE HIGH MOUNTAINS.

.LONG TERM...MODELS SHOW AN UPPER TROUGH OR CLOSED LOW OVER THE
CWA SUNDAY THROUGH MONDAY NIGHT. THE FLOW ALOFT IS PRETTY WEAK
THROUGH THE PERIODS. IT IS SOUTHERLY ON SUNDAY INTO SUNDAY
EVENING...THEN WESTERLY BY MONDAY...THEN NORTHEASTERLY MONDAY
NIGHT. AGAIN WEAK THROUGHOUT. THE SYNOPTIC SCALE ENERGY IS
SOMEWHAT CONVOLUTED ACCORDING TO THE QG VERTICAL VELOCITY FIELDS.
OVERALL...WEAK UPWARD MOTION IS PROGGED OVER THE CWA MUCH OF THE
TIME. FOR THE MOST PART...THE BOUNDARY LAYER FLOW IS NORTHWESTERLY
SUNDAY THROUGH MONDAY NIGHT. SOME OF THE MODELS HINT AT NEAR
NORTHERLY FLOW...ESPECIALLY SUNDAY NIGHT. THERE IS QUITE A BIT OF
MOISTURE OVER THE CWA ALL FOUR PERIODS. THE BEST LOW LEVEL
MOISTURE IS PROGGED OVER THE MOUNTAINS...THEN THERE IS SOME OVER
THE EASTERN HALF OF THE PLAINS. THE DOWNSLOPING KEEPS THE
FOOTHILLS AND WESTERN PLAINS FAIRLY VOID OF LOW LEVEL MOISTURE.
THERE IS SOME CAPE PROGGED OVER THE CWA ON SUNDAY...NOTHING
EXCEEDING 600 J/KG HOWEVER. THERE IS EVEN LESS PROGGED ON MONDAY.
THE LAPSE RATES ON THE CROSS SECTIONS SHOW VARIOUS CAPS IN PLACE
THROUGH THE PERIODS. THE QPF FIELDS HAVE A TAD OF MEASURABLE
RAINFALL OVER MUCH OF THE CWA SUNDAY AND SUNDAY EVENING...THEN
JUST OVER THE MOUNTAINS SUNDAY NIGHT. THERE IS MORE INDICATED
MONDAY AND MONDAY EVENING...BUT THAT IS MAINLY ON THE GFS. SO FOR
POPS THROUGH THE FOUR PERIODS...20-50%S SHOULD DO...WITH THE
HIGHEST IN THE MOUNTAINS. WILL KEEP THUNDER IN MOST TIMES. FOR
TEMPERATURES...SUNDAY`S HIGHS ARE 4-8 C COLDER THAN TODAY`S.
MONDAY`S HIGHS ARE A TAD COLDER THAN SUNDAY`S. FOR THE LATER
DAYS...TUESDAY THROUGH FRIDAY...MODELS HAVE UPPER RIDGING TO MOVE
IN TUESDAY THROUGH THURSDAY...THEN SOUTHWESTERLY FLOW ALOFT ON
FRIDAY WITH A BIG UPPER TROUGH OVER THE WEST COAST. MOISTURE IS
LACKING.

&&

.AVIATION...VFR CONDITIONS EXPECTED IN THE DENVER AREA THROUGH
TONIGHT. SOUTHWEST WINDS SHOULD BECOME NORTH TO NORTHWEST THIS
AFTERNOON...SOME QUESTION ABOUT THE TIMING AS THEY MAY BECOME NW
DURING THE MORNING OR STAY W-SW UNTIL BETTER MIXING OCCURS THIS
AFTERNOON. WIND GUSTS OF 20-25 KNOTS LIKELY IN THE LATE AFTERNOON
AND EARLY EVENING...A CHANCE OF VARIABLE GUSTS TO 40 KNOTS FROM
THUNDERSTORM OUTFLOW BUT THOSE SHOULD BE SHORT LIVED IF THEY
OCCUR.

&&

.HYDROLOGY...ANY THUNDERSTORMS OVER THE FOOTHILLS BURN AREAS
SHOULD BE WEAK...SO NO FLOODING THREAT. ISOLATED HEAVY RAIN IS
POSSIBLE WITH STRONG THUNDERSTORMS IN THE NORTHEAST CORNER...BUT
NOT MUCH OF A FLOODING THREAT THERE EITHER.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...GIMMESTAD
LONG TERM....RJK
AVIATION...GIMMESTAD