Tornado Warning 1, NWS San Angelo, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
200 PM CST MON JAN 5 1998

WEAK SHORTWAVE CURRENTLY MOVING INTO WEST TEXAS WITH RADAR AND
SATELLITE TRENDS SHOWING AN INCREASE IN CLOUDS AND LIGHT RAIN
SOUTHWEST OF THE COUNTY WARNING AREA. THUS DESPITE TEMPORARILY
IMPROVING CONDITIONS...WILL CONTINUE A DREARY FORECAST FOR THE 1ST
PERIOD. THE SHORTWAVE WILL ALSO SLOW IN SPEED AS THE UPPER TROUGH
CONTINUES TO DIG SOUTH INTO MEXICO. THIS SLOW MOVEMENT IN COMBINATION
WITH PRECIPITABLE WATER VALUES ABOVE 150 PERCENT OF NORMAL SHOULD
ALLOW FOR A GOOD CHANCE OF RAIN AREA WIDE IN THE 1ST PERIOD. WILL
NEED MENTION OF FOG AGAIN WITH LIGHT WINDS IN ADVANCE OF THE COLD
FRONT WHICH WILL GRADUALLY PUSH THROUGH THE AREA EARLY TOMORROW
MORNING.

NGM ACTUALLY INITIALIZED THE SURFACE BEST THIS RUN...BUT SINCE ETA IS
TYPICALLY SUPERIOR IN HANDLING FRONTS...WILL BLEND THE NGM FRONTAL
FORECAST WITH THE FASTER AND STRONGER ETA/AVIATION. THIS IS BECAUSE I
EXPECT BEST PVA TO SHIFT SOUTH WHERE FASTER FLOW WILL OCCUR AT THE
BASE OF THE UPPER TROUGH. AS PVA DECREASES OVER EASTERN NEW MEXICO...
EXPECT THE SURFACE TROUGH CURRENTLY OVER EASTERN PORTIONS OF COLORADO
AND NEW MEXICO TO GIVE WAY EASILY TO THE FRONT SINCE IT IS NOT THAT
STRONG TO BEGIN WITH.

MODELS SHOW GOOD AGREEMENT THROUGH THE 1ST COUPLE PERIODS WITH THE
DEEPENING OF THE UPPER LEVEL SHORTWAVE TROUGH OVER THE SOUTH CENTRAL
US AND MEXICO. MODELS ALSO AGREE ON THE TIMING OF THE INITIAL MID
LEVEL SHORTWAVE MOVING ACROSS THE FORECAST AREA BY THIS EVENING...
GIVING THE BEST CHANCE OF PRECIPITATION LATE THIS AFTERNOON AND EARLY
THIS EVENING. THIS FITS WELL WITH THE CURRENT TRENDS. AS THE FRONT
AND UPPER TROUGH BOTH BUILD SOUTH...EXPECT FOCUS FOR RAIN TO SHIFT AS
WELL SO WILL KEEP WETTEST POPS IN THE JCT AREA IN THE 2ND PERIOD.
EXPECT FRONT TO REACH SJT BY 12Z TUESDAY BUT WITH LITTLE TIME TO DRY
DEWPOINTS AND EFFECT TEMPS THROUGH 14Z. THUS WILL STAY ABOVE
GUIDANCES HERE AND AT JCT WITH MODERATE NORTHWEST WINDS HAVING
TROUBLE DRYING OUT SUCH HIGH DEWPOINTS. WILL NOT ARGUE WITH 2ND
PERIOD POPS DUE TO UNCERTAINTY OF LOW CLOUDS AND FOG WHICH COULD BE
AFFECTED BY HOW MUCH RAIN HAS FALLEN OVERNIGHT. SO FAR PRECIP AMOUNTS
ACROSS THE AREA OVER THE PAST FEW DAYS HAS BEEN VERY LIGHT. EXPECT
RAINFALL AVERAGES LESS THAN 1/4 INCH TONIGHT SINCE SURFACE FOCUSING
MECHANISMS WILL BE HARD TO COME BY. WITH NO LLJ TO SPEAK OF...EXPECT
ONLY VERY WEAK AND BRIEF EMBEDDED THUNDERSTORMS TO BE POSSIBLE
TONIGHT WITH INSTABILITY BEING THE ONLY HELP.

ABI 044/054 52
SJT 049/057 53
JCT 054/058 55

15