AREA FORECAST DISCUSSION
NWS DODGE CITY KS
AFDDDC 230 PM CST SUN MAR 19 2000
THE FORECAST TODAY PROVIDES SEVERAL OPPORTUNITIES FOR GRIEVOUS
ERROR, AND CONFIDENCE IS REASONABLY HIGH THAT THE ATMOSPHERE WILL
NOT BEHAVE EXACTLY AS PLANNED. AMONG THE POTENTIAL PITFALLS ARE THE
FOLLOWING: 1) THE EFFECT OF CIRRIFORM CLOUDINESS AND THE RESIDUAL
POOL OF COOL, MOIST AIR OVER THE CENTRAL UNITED STATES ON MAXIMUM
TEMPERATURES MONDAY; 2) THE ARRIVAL OF LOW LEVEL GULF MOISTURE
MONDAY NIGHT/EARLY TUESDAY AND ITS DRAMATIC EFFECT ON MINIMUM
TEMPERATURES; AND 3) THE ONSET AND EXTENT OF PRECIPITATION MONDAY
NIGHT AND TUESDAY.
THE DEEP CLOSED UPPER LEVEL LOW PRESSURE SYSTEM WHICH WAS CENTERED
NEAR THE MISSOURI/IOWA BORDER EARLY THIS AFTERNOON WITH AN INTENSE
VORTICITY MAXIMUM ROTATING OVER THE GULF COAST BEHAVED MUCH AS HAD
BEEN FORECAST BY THE MODELS. THE AVN SEEMED TO HAVE THE BEST HANDLE
ON THE DOUBLE COLD POOL EVIDENT ON 12Z ANALYSES AND THE POSITION OF
THE H5 LOW WHICH WAS OVER SOUTHEASTERN KANSAS AT 12Z.
THE DEEP UPPER LEVEL WAVE WHICH WAS AROUND 145 DEGREES WEST AT THIS
TIME SATURDAY HAS DROPPED SOUTHEASTWARD INTO THE NORTHWESTERN UNITED
STATES IN RESPONSE TO STRONG RIDGING IN THE GULF OF ALASKA AROUND
140 DEGREES WEST. NONE OF THE NUMERICAL MODELS WERE LOW ENOUGH ON
HEIGHTS OR TEMPERATURES IN THE NORTHWESTERN UNITED STATES, BUT THE
AVN ONCE AGAIN SUBJECTIVELY WAS SOMEWHAT CLOSER TO REALITY. ALL OF
THE NUMERICAL SOLUTIONS INITIALIZED SIMILARLY WITH HIGH LEVEL FLOW
OVER THE EASTERN PACIFIC AND ARE IN GOOD AGREEMENT WITH AVAILABLE
OBSERVATIONAL DATA. THE AVN ANALYSIS DEPICTED A SLIGHTLY STRONGER
JET ON THE WEST SIDE OF THE GULF OF ALASKA RIDGE THAN THE RGL,
PROBABLY REFLECTING ADDITIONAL AIRCRAFT REPORTS BEFORE DATA CUTOFF
TIME.
ALL OF THE MODELS ARE SIMILAR IN DROPPING THE INTENSE NORTHWESTERN
UNITED STATES WAVE INTO THE SOUTHWESTERN PART OF THE COUNTRY AND
CLOSING IT OFF. THE RGL IS SOMEWHAT DEEPER WITH THE CLOSED LOW THAN
EITHER THE ETA, AVN OR CANADIAN SPECTRAL AND MAY BE SLIGHTLY
OVERDONE WITH THE STRENGTH OF THE SYSTEM. THE RGL ALSO IS UNIQUE IN
DEVELOPING AN INTENSE SURFACE CYCLONE IN NEW MEXICO, SUBSEQUENTLY
REDEVELOPING THE CYCLONE NEAR THE FOUR CORNERS AREA, THEN BACK INTO
ARIZONA. THE AVN/ETA SOLUTIONS ARE MUCH MORE PHYSICALLY REASONABLE
AND ARE PREFERRED. THE AVN, EVEN MORE THAN THE ETA, SEEMS TO HAVE A
GOOD HANDLE ON DEVELOPMENT OF A LARGE SCALE DENSITY CURRENT IN THE
LEE OF THE ROCKIES IN RESPONSE TO AN EXTENDED PERIOD OF DEEP
EASTERLY FLOW AGAINST THE TERRAIN. GIVEN THE PAST PERFORMANCE OF THE
AVN, ITS APPARENT BETTER INITIALIZATION, AND ITS MODELING OF THE
SURFACE PATTERN IN THE LEE OF THE ROCKIES, THE AVN WILL BE THE MODEL
OF CHOICE FOR THE AFTERNOON PACKAGE.
PRESSURES WERE DROPPING NICELY IN THE LEE OF THE ROCKIES EARLY THIS
AFTERNOON IN RESPONSE TO INCREASING FLOW PERPENDICULAR TO THE
MOUNTAINS. LOW LEVEL SOUTHERLY FLOW SHOULD CONTINUE TO INCREASE THIS
AFTERNOON AND REMAIN IN THE 10 TO 20 KNOT RANGE THROUGH THE NIGHT.
MIXING SHOULD BE SUFFICIENT TO KEEP TEMPERATURES RELATIVELY MILD
EVEN WITH QUITE DRY AIR IN THE LOWER LEVELS OF THE ATMOSPHERE. MOS
TEMPERATURES SEEM REASONABLE EXCEPT FOR THE EASTERN ZONES WHERE
GUIDANCE SEEMS A FEW DEGREES TOO HIGH.
CYCLOGENESIS OVER NEW MEXICO MONDAY WILL RESULT IN A TIGHT PRESSURE
GRADIENT OVER WESTERN KANSAS, AND THE "WINDY" PHRASEOLOGY IN THE
GOING FORECAST STILL LOOKS GOOD. THE EXTENSIVE AREA OF COOL, MOIST
AIR ROTATING AROUND THE UPPER LEVEL LOW PRESSURE SYSTEM OVER
NORTHERN MISSOURI MAY SPREAD BACK WESTWARD MONDAY AND KEEP
TEMPERATURES SOMEWHAT LOWER THAN ORIGINALLY PLANNED FOR THE NORTHERN
ZONES. THE REMAINDER OF THE AREA, HOWEVER, SHOULD WARM UP NICELY
WITH H8 TEMPERATURES IN THE 15-20 DEGREE RANGE OVER THE SOUTHWESTERN
ZONES. CIRRIFORM CLOUDINESS WILL BE WIDESPREAD BUT PROBABLY WILL BE
THIN ENOUGH TO ALLOW ABUNDANT INSOLATION. MOS SEEMS A LITTLE ON THE
COOL SIDE, AND SLIGHTLY WARMER TEMPERATURES WILL BE CARRIED IN THE
ZONE PACKAGE.
LOW LEVEL MOISTURE WILL BEGIN TO SPREAD NORTHWARD ON MONDAY AND
LIKELY WILL REACH SOUTHWESTERN KANSAS MONDAY NIGHT. UPSLOPE FLOW,
ISENTROPIC LIFTING AND MINOR WAVES ROTATING AROUND THE CLOSED UPPER
LEVEL LOW WILL COMBINE TO PRODUCE WIDESPREAD RAINFALL MONDAY NIGHT
AND TUESDAY. THE BEST CONVERGENCE AND LIFTING WILL BE CONCENTRATED
OVER THE WESTERN PART OF THE DODGE CITY AREA OF RESPONSIBILITY, AND
HIGHEST POPS WILL BE CARRIED THERE. ENOUGH MID LEVEL INSTABILITY IS
EVIDENT IN MODEL SOUNDINGS TO SUPPORT SOME EMBEDDED CONVECTION, BUT
GENERAL STRATIFORM RAIN WILL BE THE MORE FAVORED MODE. TEMPERATURES
WILL BE FAR TOO WARM TO SUPPORT ANY FROZEN PRECIPITATION.
EXTENDED DISCUSSION...
EARLY PERIODS OF THE EXTENDED FIND THE MEDIUM RANGE MODELS IN QUITE
GOOD AGREEMENT BUT THINGS GET MORE DOUBTFUL WITH TIME. BY FRIDAY
MORNING THE ECMWF ATTEMPTS LIFT THE UPPER LOW RAPIDLY NORTHEAST AND
PHASE IT INTO NORTHERN BRANCH FLOW. THIS APPEARS UNLIKELY AND
PREFER TO FOLLOW THE MRF MORE CLOSELY IN LIFTING THIS FEATURE OUT
MORE SLOWLY AND KEEPING IT TIED TO THE SOUTHERN BRANCH OF THE
WESTERLIES. THIS SYSTEM DOES NOT APPEAR TO TAP ANY TRUE ARCTIC AIR
BUT THE MRF LOOKS AWFULLY WARM IN THE LOW LEVELS FOR SATURDAY AND
SUNDAY AS THE NEXT UPSTREAM SYSTEM DIGS INTO THE WEST COAST. ALL IN
ALL THE WEEK LOOKS WET FOR THE PLAINS AS THE UPPER LOW OVER THE
SOUTHWEST ON MONDAY AND TUESDAY WRAPS ITS DEFORMATION ZONE ACROSS
THE REGION AND ROTATES SPOKE AFTER SPOKE OF VORT OUT INTO THE PLAINS
WHERE COPIOUS MOISTURE FROM THE GULF OF MEXICO RESIDES. ELEVATED
EMBEDDED CONVECTION CONTINUES TO BE A POSSIBILITY SO WILL KEEP SOME
MENTION OF THUNDERSTORMS. A FAIRLY RAPIDLY MOVING SHORT WAVE RIDGE
ACROSS THE REGION ON SATURDAY WILL LIKELY SHUT OFF CHANCES FOR
PRECIPITATION BUT BY SUNDAY AFTERNOON THE NEXT SYSTEM UPSTREAM
EJECTS ENERGY INTO THE PLAINS TO MEET ONCE AGAIN WITH GULF MOISTURE
AND WILL EXPECT CONVECTION ON SUNDAY AFTERNOON AGAIN. CLOUD COVER
ACROSS THE REGION THROUGH THURSDAY WILL REQUIRE TRIMMING HIGH
TEMPERATURES BACK BELOW THE FMR NUMBERS WHEREAS LOWS LOOK FAIRLY
REASONABLE. THE STRENGTH OF THE WARM AIR ADVECTION FROM TUESDAY
THROUGH THURSDAY AND CORRESPONDINGLY HIGH THICKNESS VALUES DICTATE
THE PRECIPITATION WILL BE LIQUID. BY FRIDAY WITH THE SURFACE LOW
MOVING SOMEWHERE OFF TO THE EAST AND WITH NORTHERLY FLOW ACROSS THE
REGION IT IS HARD TO SEE TEMPERATURES WARMING AS MUCH AS THE FMR BUT
FMR NUMBERS FOR SATURDAY AND SUNDAY APPEAR TO BE IN THE BALL PARK
GIVEN THE AMOUNT OF INSOLATION AT THIS TIME OF YEAR.
PRELIMINARY GUIDANCE FOR COORDINATION ONLY. OFFICIAL FORECASTS ARE
CONTAINED WITHIN THE DODGE CITY ZONE FORECAST.
DDC 036/063 043/051 045 004
GCK 034/065 040/051 044 005
EHA 034/070 038/049 043 006
LBL 036/068 043/053 046 005
HYS 035/061 039/052 043 003
P28 035/066 047/056 048 002
.DDC...NONE.
01/JOHNSON