A weak frontal boundary across the Baltimore/Washington DC metros led to southerly flow off the Atlantic and moisture to move into the region. Dense fog formed over parts of southern Maryland.
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The episode as NWS LWX wrote it up.
A weak frontal boundary across the Baltimore/Washington DC metros led to southerly flow off the Atlantic and moisture to move into the region. Dense fog formed over parts of southern Maryland.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Baltimore/Washington wrote its last area forecast discussion before the first event at Dec 1, 3:41 AM EST, 6 hours 39 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 341 AM EST SAT DEC 1 2012 .SYNOPSIS... A BACKDOOR COLD FRONT DRAPED ACROSS THE AREA EARLY THIS MORNING WILL RETREAT NORTH AS A WARM FRONT TODAY. HIGH PRESSURE WILL BUILD SOUTHEAST OF THE AREA TONIGHT AND SUNDAY. A WEAK COLD FRONT WILL MOVE EAST THROUGH THE REGION SUNDAY NIGHT. A SLIGHTLY STRONGER COLD FRONT WILL MOVE THROUGH THE MID-ATLANTIC LATE TUESDAY AND EARLY WEDNESDAY FOLLOWED BY HIGH PRESSURE THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... SHALLOW SFC CDFNT APPEARS TO BE ACRS NERN MD ATTM...AND SHUD BE SINKING SWD THRU THE ELY MRNG. LOW CLDS DVLPG ACRS ERN PA SINCE 06Z...IMPACTING AS FAR S AS THV ATTM...AND SHUD AFFECT PRIMARILY MD SPCLY BTWN I-95 AND THE CATOCTINS BY SUNRISE. FOG HAS DVLPD S OF THE BNDRY...ACRS MD ERN SHORE...AND HAS ADVECTED WWD TO THE ST MARYS/CALVERT CNTY COAST. WL NEED TO MONITOR ITS PROGRESS TOO...AS IT MAY ENGULF SRN MD. EXPANDED AREAS OF FOG IN THE GRIDS...BUT RESTRICTIONS TAKEN STILL MAY BE TOO SKIMPY. ELSW...AN H5 S/WV HAS LED TO A BAND OF CLDS. GDNC SUGGESTING THESE CLDS SHUD DEPART BY THE START OF THE DAY. SINCE FNT SHALLOW...DAYTIME MIXING SHUD ERODE ITS LOW CLDS AND FOG...THEREBY FORCING FNT TO RETREAT NWD TDA. CONSEQUENTLY...SUNSHN SHUD BE PLENTIFUL...AND HV LEANED ON THE WARMER SIDE OF GDNC. HWVR...NRN MD WL SEE THESE EFFECTS LAST SO THEY WL STILL BE ON THE COOLISH SIDE /MAXT ARND 50F/. RDGG WL TAKE HOLD AT THE SFC AND ALOFT TNGT. NRN CNTYS WL BE NEARER TO FASTER MID-LVL FLOW...SO WL PAINT SCT TO ALMOST BKN CLDS THERE. ELSW...DONT SEE ANY SGFNT FEATURE. DEWPTS SHUD BE HIER /A RSLT OF RESIDUAL MSTR FM THE PRESENT ENE FLOW/...SO HV FCST MIN-T LIKEWISE. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... SOME DEJA VU MOMENTS OVER THE COMING WEEK...AS A COUPLE OF FRONTAL PASSAGES SHAPING UP FOR THE REGION - BRIDGED BY SIMILAR BOUTS OF HIGH PRESSURE. THE FIRST FRONT WILL LARGELY WASH OUT AS IT CROSSES THE AREA OVERNIGHT SUN INTO EARLY MON. THE PARENT LOW WILL SPEED OFF TO THE NE FROM THE GREAT LAKES REGION ON SUN...LEAVING THE FRONT TO DISSIPATE AS IT CROSSES THE APLCNS SUN NIGHT. UNLIKE MOST FRONTAL PASSAGES...ESPECIALLY THIS TIME OF YEAR...IT WON'T EXACTLY BE MARKED BY A SIGNIFICANT TEMP CHANGE. IN FACT...SUN NIGHT WILL BE ONE OF THE WARMER NIGHTS IN RECENT MEMORY - ONLY DROPPING INTO THE U40S FOR OVERNIGHT LOWS. A FEW LIGHT SHOWERS MAY REAPPEAR ALONG THE I-95 CORRIDOR BEFORE THE FRONT MOVES OFF THE COAST...BUT VERY LIGHT AND SHORT LIVED. THE WARM OVERNIGHT PERIOD SUN NIGHT WILL OCCUR IN LARGE PART BECAUSE THE DAYTIME HRS ON SUN WILL HAVE HAD A GOOD SLY BREEZE IN PLACE...INCREASING THE LOW LEVEL MOISTURE. DESPITE THE WIND SHIFT W/ THE FRONT EARLY MON TOWARD THE NW...DRIER AIR WILL NOT MIX INTO THE AREA - HELPING TO KEEP TEMPS MODERATED OVERNIGHT. SAME STORY ON MON...AS THE SFC HIGH REESTABLISHES ITSELF OVER THE EAST COAST AND SENDS ANOTHER SEVERAL HRS OF WARM/MOIST SLY WINDS UP THE ERN SEABOARD. TEMPS WILL MAKE THEIR WAY WELL INTO THE 60S ACROSS THE REGION ON MON AFTN...WHICH WILL SET US UP FOR YET ANOTHER RELATIVELY WARM OVERNIGHT PERIOD...W/ LOWS BARELY DROPPING INTO THE 40S. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AN ENCORE OF MON WILL BE ON TUE...AHEAD OF A SIMILAR FRONTAL PASSAGE ON WED. THE FRONT ON WED MAY BRING A BIT MORE SHOWER ACTIVITY TO THE AREA...AND MOVE THRU ON WED MRNG. THIS FRONT HOWEVER...WILL BRING A NOTICEABLE TEMP CHANGE - DROPPING HIGHS AND LOWS DOWN ABOUT 10-15 DEGREES FOR THE NEXT COUPLE OF DAYS. THIS PASSAGE WILL BE AIDED BY A STRONGER PARENT LOW PRESSURE SYSTEM OVER THE GREAT LAKES THAT WILL TAP INTO A BETTER COLD CANADIAN AIR FETCH. OVER THE LONGER TERM...IT APPEARS THAT A SLIGHTLY STRONGER SYSTEM THAN THIS ONE WILL THEN MAKES AN DIVE TOWARD THE AREA BY THE END OF THE COMING WEEK. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... CHALLENGING AVN FCST FOR THIS MRNG. OBS HV BEEN MORE BENIGN THAN FCST...BUT MVFR/IFR FOG NAK S/EWD AND AOB IFR CIGS ACRS PA. GDNC INSISTENT THAT RESTRICTIONS WL NOT REACH TERMINALS. AM NOT SURE THAT WL VERIFY BEST. CUD SEE LOW CLDS DVLP W OF BWI/MTN/DCA AND JUST NNE OF IAD. GOING TAFS HV SCT IFR CLDS IN THESE AREAS TO ACCT FOR THAT POTL. CUD ALSO SEE FOG SPREADING WNWWD. LEFT MVFR VSBYS IN THE BWI TAF FOR THAT RISK. ANTICIPATE TAFS WL REQ AMD THRU THE ELY MRNG. WHATEVER RESTRICTIONS DO DVLP ELY THIS MRNG WL MIX OUT SUNRISE TO MID-MRNG. VFR SHUD PREVAIL REST OF DAY. FOG DVLPMNT SHUDNT BE AS WDSPRD TNGT...BUT ITS A PSBLTY AT CLIMO FVRD CHO...WHERE RADIATIONAL COOLING WL BE BEST SINCE THATS WHERE CLDCVR WL BE THE LEAST. A WEAK FRONTAL BOUNDARY WILL SLIDE THRU THE AREA DURING THE PREDAWN HRS MON...SHIFTING WINDS FROM SLY TO NWLY BY THE MID MRNG HRS... THOUGH THE MAGNITUDES WILL DECREASE. HIGH PRESSURE WILL BUILD FOR MON AND TUE...THEN A COLD FRONT WILL MOVE THRU ON WED W/ STRONGER NWLY WINDS GUSTS IN THE 15-25KT RANGE. CONDITIONS WILL SUBSIDE AGAIN OVERNIGHT AS HIGH PRESSURE BUILDS IN FOR THU AND INTO FRI. && .MARINE... FOG ACRS WATERS ELY THIS MRNG...SPCLY MID BAY AND LWR PTMC. XPCT IMPVMNT AFTER DAYBREAK. OTRW NO SGFNT WX TDA-TNGT. NE WNDS AOB 10 KT TDA BCMG SELY TNGT. HIGH PRESSURE WILL BE IN PLACE FOR MUCH OF THE WEEK...THOUGH A COUPLE OF FRONTAL PASSAGES WILL IMPACT THE AREA. THE FIRST FRONT WILL MAKE LITTLE IMPACT OTHER THAN TO CHANGE THE WIND DIRECTION ON MON MRNG...FROM SLY TO NWLY. THE FRONT ON WED MRNG WILL BRING THE SAME CHANGE...THOUGH WINDS WILL BE BREEZY ACROSS THE WATERS FOR MUCH OF THE DAY. WINDS WILL TAPER OFF HEADING INTO NEXT WEEKEND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...GMS LONG TERM...GMS AVIATION...HTS/GMS MARINE...HTS/GMS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 500 AM EST SAT DEC 1 2012 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 021000- CHESAPEAKE BAY NORTH OF POOLES ISLAND MD- CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD- CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD- CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD- CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA- TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD- TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD- TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA- PATAPSCO RIVER INCLUDING BALTIMORE HARBOR- CHESTER RIVER TO QUEENSTOWN MD-EASTERN BAY- CHOPTANK RIVER TO CAMBRIDGE MD AND THE LITTLE CHOPTANK RIVER- PATUXENT RIVER TO BROOMES ISLAND MD- TANGIER SOUND AND THE INLAND WATERS SURROUNDING BLOODSWORTH ISLAND-DISTRICT OF COLUMBIA-NORTHERN BALTIMORE-HARFORD- SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS- CALVERT-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX- ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA- KING GEORGE- 500 AM EST SAT DEC 1 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MARYLAND PORTION OF THE CHESAPEAKE BAY...TIDAL POTOMAC RIVER...AND ADJACENT COUNTIES IN CENTRAL MARYLAND AND NORTHERN VIRGINIA AS WELL AS THE DISTRICT OF COLUMBIA. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504- WVZ050>053-055-501>506-021000- WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD- EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-AUGUSTA- ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-NELSON- ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER- NORTHERN FAUQUIER-SOUTHERN FAUQUIER-WESTERN HIGHLAND- EASTERN HIGHLAND-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY- WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL- WESTERN PENDLETON-EASTERN PENDLETON- 500 AM EST SAT DEC 1 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN WEST VIRGINIA... NORTHERN AND CENTRAL VIRGINIA...AND CENTRAL AND WESTERN MARYLAND WITH THE EXCEPTION OF GARRETT COUNTY. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 742 AM EST SAT DEC 1 2012 MDZ014-016>018-011500- ANNE ARUNDEL-CHARLES-ST. MARYS-CALVERT- INCLUDING THE CITIES OF...ANNAPOLIS...WALDORF...ST MARYS CITY 742 AM EST SAT DEC 1 2012 ...PATCHY DENSE FOG ALONG COASTAL LOCATIONS OF SOUTHERN MARYLAND... PATCHY DENSE FOG WILL AFFECT PORTIONS OF SOUTHERN MARYLAND THROUGH MID MORNING...PARTICULARLY NEAR COASTAL LOCATIONS ALONG THE WESTERN SHORE OF CHESAPEAKE BAY...THE PATUXENT RIVER AND THE LOWER TIDAL POTOMAC RIVER. VISIBILITIES WILL BE LOCALLY REDUCED TO ONE- QUARTER MILE. WHEN DRIVING THIS MORNING...SLOW DOWN...USE YOUR LOW-BEAM HEADLIGHTS AND BE PREPARED FOR A SUDDEN REDUCTION OF VISIBILITY IN FOG PRONE AREAS. JRK
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 939 AM EST SAT DEC 1 2012 DCZ001-MDZ004>007-009>011-013-014-016>018-VAZ042-054-057-011700- DISTRICT OF COLUMBIA-FREDERICK MD-CARROLL-NORTHERN BALTIMORE- HARFORD-MONTGOMERY-HOWARD-SOUTHERN BALTIMORE-PRINCE GEORGES- ANNE ARUNDEL-CHARLES-ST. MARYS-CALVERT-LOUDOUN- ARLINGTON/FALLS CHURCH/ALEXANDRIA-KING GEORGE- INCLUDING THE CITIES OF...WASHINGTON...FREDERICK...WESTMINSTER... GAITHERSBURG...COLUMBIA...BALTIMORE...ANNAPOLIS...WALDORF... ST MARYS CITY...LEESBURG...ALEXANDRIA...FALLS CHURCH 939 AM EST SAT DEC 1 2012 ...PATCHY DENSE FOG ACROSS PORTIONS OF THE METROPOLITAN AREA THIS MORNING... PATCHY DENSE FOG WILL AFFECT LOWER SOUTHERN MARYLAND AND PORTIONS OF THE METROPOLITAN AREAS OF WASHINGTON DC AND THE CITY OF BALTIMORE THIS MORNING. VISIBILITIES WILL BE LOCALLY REDUCED TO ONE- QUARTER MILE. WHEN DRIVING THIS MORNING...SLOW DOWN...USE YOUR LOW-BEAM HEADLIGHTS AND BE PREPARED FOR A SUDDEN REDUCTION OF VISIBILITY IN FOG PRONE AREAS.
The national radar mosaic for the moment the first event began.
1 dense fog. Local standard time, as filed.
Visibility was reported to be around one quarter mile at Patuxent River NAS and St Mary's Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2012Every state in 2012This day in weather historyWarnings in Maryland, December 2012
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 425691.