Severe Thunderstorm Warning 4, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
150 PM CDT MON MAY 3 1999

TIMING OF PRECIPITATION WILL BE THE MAIN CHALLENGE THROUGH THE PERIOD.

17Z SURFACE ANALYSIS SHOWS A DEEP LOW PRESSURE TROUGH EXTENDING FROM
THE EXTREME WESTERN DAKOTAS INTO EASTERN WYOMING AND EASTERN COLORADO
WITH A LOWEST PRESSURE NEAR LARAMIE.  SFC DEWPOINTS ARE IMPRESSIVE FROM
KANSAS INTO EASTERN NEBRASKA. ONEILL REPORTING A 55 DEWPOINT. EXPECT
CONVERGENCE ALONG THIS SFC TROUGH THIS EVENING AND TONIGHT.

12Z MODEL RUNS SHOW GOOD AGREEMENT INITIALLY WITH THE PLACEMENT OF THE
500 MB TROUGHS.  500 MB HAND ANALYSIS SHOWS NEXT SHORTWAVE EXTENDING
FROM SW UTAH INTO WESTERN AZ.  GOOD MOISTURE AT 500 MB FROM DESERT SW
INTO THE INTERMOUNTAIN REGION.

COMPARING MODELS THROUGH 48 HOURS...THE ETA DIFFERS TO MOST. BY 48 HRS
THE NGM AND AVN ARE IN GOOD AGREEMENT WITH PLACEMENT OF THE UPPER
TROUGH WITH THE NGM SHOWING A SLIGHTLY DEEPER CLOSED LOW OF 540 MB. THE
ETA IS THE WEAKEST WITH UPPER TROUGH AND SHOWS A CLOSED LOW OF 551 MB
BY 48 HRS. PREFER AN NGM-AVN COMPROMISE AT BOTH THE SURFACE AND ALOFT.
BY 48 HRS THE ETA HAS THE SURFACE LOW IN NW MO WHILE THE AVN AND NGM
SHOW THE SFC LOW NEAR SIOUX CITY.

RAIN CHANCES LOOK ACROSS THE FA TONIGHT THROUGH TUESDAY NIGHT. THIS
EVENING 850-500 DIV Q AND OGEGA SET UP FROM CENTRAL AND EASTERN NE INTO
SD AS SFC TROUGH SWINGS OUT OF SW NEBRASKA AND NORTHEASTWARD. STRONG
CAP TO BREAK AS 18Z OAX SOUNDING TAKEN SHOWS THIS. STRONG DIV Q SETS UP
IN WESTERN NEBRASKA BY 12Z TUES AS A SFC LOW DEEPENS AND UPPER TROUGH
APPROACHES. ALSO A STRONG JET MAX MOVING FROM NORTHERN CA WILL STREAM
EAST AND BY 24 HRS A JET COUPLET SHOULD FORM BETWEEN THE SOUTHERN JET
AND A WEAKER NORTHERN JET NOSING INTO WESTERN ND HELPING TO FORM THE
SURFACE LOW.

WILL CARRY CHANCE OF SHOWERS AND THUNDERSTORMS TONIGHT THROUGH THUESDAY
NIGHT.  THE BEST CHANCE WILL BE IN ANW TO BROKEN BW EAST THIS EVENING
AND THEN OVERNIGHT WILL WORD SHOWERS AND THUNDERSTORMS LIKELY IN THE
WEST AND LIKELY ACROSS THE FORECAST AREA ON TUESDAY. TUESDAY NIGHT
THUNDERSTORMS SHOULD END IN SOUTHWEST NEBRASKA BUT CONTINUE INTO
WEDNESDAY MORNING ELSEWHERE.

GOOD MOISTURE 1000-500 MB 24-48 HOURS.  HIGH TEMPS WILL NEED TO BE
TRIMMED BACK ON NGM MOS TUES AND WED WITH MAINLY CLOUDY SKIES AND
SHOWERS TUESDAY. COOLER TEMPS WED AS NGM THICKNESSES DROP TO 537 DAM IN
THE PANHANDLE. A RAIN-SNOW MIX NOT OUT OF THE QUESTION IN NW NEBRASKA.

ROBERG