Sunday through Wednesday Forecast Discussion

By: NWS
By: NWS

MAIN ISSUES OF CONCERN FOR THE EXTENDED PORTION OF THE FORECAST DEAL WITH THE PASSAGE OF A STRONG COLD FRONT FRIDAY NIGHT INTO SATURDAY AND THEN THE POTENTIAL FOR COLD NIGHTS BOTH SATURDAY INTO EARLY SUNDAY AND SUNDAY INTO EARLY MONDAY. WE BEGIN SATURDAY WITH A HIGHLY AMPLIFIED UPPER LEVEL PATTERN ACROSS THE CONUS WITH LARGE SCALE RIDGING ALONG THE PACIFIC COAST/ INTERMOUNTAIN WEST AND DEEP TROUGHING DIGGING INTO THE EASTERN HALF OF THE NATION. THIS TROUGH WILL BE DELIVERING A STRONG SHOT OF POLAR AIR TO THE CENTRAL PLAINS EASTWARD TO THE ATLANTIC COAST BY SUNDAY MORNING. GLOBAL GUIDANCE GFS/ECMWF BOTH SHOWING A STRONG SURFACE COLD FRONT ENTERING THE SE U.S. FRIDAY EVENING AND THEN CROSSING RAPIDLY THROUGH THE FORECAST AREA FRIDAY NIGHT/SATURDAY MORNING. SHOWERS/AND OR THUNDERSTORMS AHEAD OF THIS FRONT WILL BE ENDING EARLY SATURDAY MORNING AS MUCH DRIER AIR RAPIDLY ADVECTS OVERHEAD. WILL ALSO BE LOOKING AT STRONG COLD AIR ADVECTION INTO THE AREA BEHIND THIS FRONT THROUGH SATURDAY NIGHT. GFS/ECMWF BOTH SHOWING 850MB TEMPS FALLING FROM +10 TO +14C (NW TO SE) EARLY SATURDAY MORNING DOWN TO BETWEEN -2 AND +4C BY EARLY SUNDAY MORNING. AFTER AN EARLY MORNING SHOWER OVER THE SE HALF OF THE AREA WILL EXPECT GENERALLY A FAIR WEATHER DAY SATURDAY WITH PARTLY SUNNY SKIES AND GUSTY NW WINDS. STRONG MIXING IN THE IMMEDIATE WAKE OF THE FRONT SHOULD STILL ALLOW FOR TEMPS TO REACH THE MIDDLE 60S NORTHWEST AND UPPER 60S TO LOWER 70S SOUTHEAST DESPITE THE COLD AIR ADVECTION. THIS AIRMASS WILL REALLY BEGIN TO BE FELT AFTER SUNDOWN SATURDAY EVENING. LATEST BIAS CORRECTED GRIDS SHOWING WIDESPREAD TEMPERATURES DROPPING INTO THE MIDDLE AND UPPER 30S BY SUNRISE SUNDAY MORNING (EVEN RIGHT TO THE COAST WITH THE TIGHT NW GRADIENT). AT THIS POINT THE DEGREE OF CAA DOES NOT LOOK TO BE ENOUGH TO BRING TEMPS DOWN TO FREEZING AND WITH NW WINDS KEEPING THE LOW LEVELS MIXED...FROST APPEARS UNLIKELY. HOWEVER...WITH THE WINDS STAYING UP AND TEMPS DROPPING THROUGH THE 40S AND POTENTIALLY INTO THE 30S...IT IS LIKELY TO FEEL QUITE COOL SATURDAY NIGHT FOR ANY OUTDOOR ACTIVITIES. STRONG 1025-1029MB SURFACE RIDGE IS THEN EXPECTED TO MOVE EAST ALONG THE NORTHERN GULF COAST SUNDAY INTO MONDAY. 850MB TEMPS IN THE +3 TO +6C RANGE DURING THE DAY SUNDAY WILL KEEP TEMPS ON THE COOLER SIDE WITH AFTERNOON HIGHS STRUGGLING INTO THE LOWER 60S NORTH AND MIDDLE 60S SOUTH... DESPITE MOSTLY SUNNY SKIES. IF A FROST OR FREEZE EVENT IS GOING TO OCCUR WITH THIS COLD AIR OUTBREAK THE BEST CHANCE APPEARS TO BE SUNDAY NIGHT INTO EARLY MONDAY AS SURFACE RIDGING BUILDS CLOSER AND ALLOWS FOR A BETTER RADIATIONAL COOLING SETUP. MEX GUIDANCE INDICATING WIDESPREAD UPPER 30S DESPITE A SIGNIFICANT AMOUNT OF MIDDLE TO UPPER 40S CLIMATOLOGY BUILD IN. THIS WOULD SUGGEST TEMPERATURES FALLING EVEN LOWER. THIS EVEN LOWER TEMP POSSIBILITY IS CONFIRMED BY THE BIAS CORRECTED GRIDS WHICH SHOW WIDESPREAD LOWER AND MIDDLE 30S...AND NORMALLY COLDER INLAND SPOTS POTENTIALLY REACHING INTO THE LOWER 30S. THESE CALMER CONDITIONS WILL BE MORE CONDUCIVE TO AREAS OF FROST FORMATION. AFTER A BRIEF WARM-UP BACK TOWARD NORMAL ON TUESDAY...A DRY COLD FRONT IS PROGGED TO CROSS THE SOUTHEAST STATES LATE IN THE DAY OR AT NIGHT WITH A RE-ENFORCING SHOT OF POLAR AIR. $$


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