PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300 PM EST THU JAN 31 2019 30-DAY OUTLOOK DISCUSSION FOR FEBRUARY 2019 THE UPDATED FEBRUARY 2019 TEMPERATURE OUTLOOK DEPICTS SUBSTANTIAL CHANGES FROM THE MID-MONTH OUTLOOK RELEASED TWO WEEKS AGO. CONSIDERABLE VARIABILITY ANTICIPATED DURING AT LEAST THE FIRST HALF OF THE MONTH MAKES FOR A CHALLENGING OUTLOOK. RIGHT AT THE START OF THE MONTH, THE HIGHLY AMPLIFIED, POTENT TROUGH RESPONSIBLE FOR MUCH BELOW-NORMAL AND RECORD COLD TEMPERATURES FOR MUCH OF THE CENTRAL AND EASTERN CONUS LIFTS OUT AND IS REPLACED WITH A VERY IMPRESSIVE, RAPID WARMUP, FIRST ACROSS THE WESTERN AND CENTRAL CONUS, THEN ACROSS THE EASTERN CONUS FROM THE SOUTHEAST TO MAINE. ALTHOUGH THERE IS STILL CONSIDERABLE DIFFERENCES IN THE NEXT STRONG TROUGH TO AMPLIFY AND EXTEND ACROSS THE CONUS, IT IS MOST LIKELY THAT A STRONG TROUGH MAY ORIENT ITSELF FROM CENTRAL CANADA SOUTHWESTWARD TO THE SOUTHWEST CONUS POSITIONING HIGH ODDS FOR BELOW-NORMAL TEMPERATURES FARTHER WEST ACROSS FROM THE NORTHERN PLAINS TO PARTS OF THE SOUTHWEST. THIS AREA THEN SLOWLY EXTENDS AND SHIFTS TO THE EAST AND SLIGHTLY TO THE NORTH WITH TIME AND THE UNCERTAINTY INCREASES DURING THE FINAL TWO WEEKS, AS IS TYPICAL, BUT IT APPEARS THAT TROUGHING, IN THE MEAN, MAY PERSIST ACROSS THE NORTH CENTRAL CONUS, WITH TYPICAL VARIABILITY IN SHORT WAVE TROUGHS ABOUT THIS MEAN POSITION, INTO THE EASTERN CONUS AT TIMES. THE OFFICIAL TEMPERATURE OUTLOOK FAVORS BELOW-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN AND CENTRAL CONUS HIGHLIGHTING THAT EARLY MONTH WARMTH IS MOST LIKELY TO BE OVERCOME IN THESE AREAS BY THE AFOREMENTIONED STRONG TROUGH DEVELOPMENT ACROSS THE WEST CENTRAL CONUS ENTERING WEEK-2. THE GREATEST PROBABILITIES ARE LOCATED ACROSS THE NORTHERN PLAINS AND NORTHERN ROCKIES AS THESE AREAS ARE MOST LIKELY TO BE IN FAVORED AREAS OF BELOW-NORMAL TEMPERATURES FOR THE MAJORITY OF THE MONTH. ALTHOUGH CONSIDERABLY ABOVE-NORMAL TEMPERATURES ARE FAVORED FOR THE SOUTHEAST AND EASTERN SEABOARD DURING THE FIRST WEEK OF FEBRUARY, THE UNCERTAINTY AND VARIABILITY IN TROUGHING AND THE PHASE OF THE AO INDEX (CONTINUED IMPACT FROM THE SSW EVENT AT THE TURN OF THE YEAR) ACROSS THE EASTERN CONUS, RESULTS IN A DEPICTION OF "EC" FOR THE NORTHEAST AND NEARBY AREAS AND ONLY MODEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES FOR THE SOUTHEAST AND LOWER MID-ATLANTIC - WHERE THERE IS A GREATER LIKELIHOOD THAT EARLY MONTH WARMTH MAY HANG ON FOR THE EVENTUAL OBSERVED MONTHLY MEAN TEMPERATURES. THE FAVORED PATTERN TO AFFECT ALASKA SUPPORTS ANOMALOUS RIDGING AND ANOMALOUS SOUTHWESTERLY FLOW AND SO ELEVATED ODDS OF ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR MOST OF THE STATE FOR FEBRUARY. SIMILAR TO THE TEMPERATURE OUTLOOK, THE PRECIPITATION FORECAST IS SIGNIFICANTLY CHANGED FROM THE MID MONTH RELEASE. THE ANTICIPATED WEST-CENTRAL MEAN TROUGH AND INDICATIONS OF A CONTINUED ENERGIZED SOUTHERN STREAM DURING PERIODS OF THE FIRST HALF OF FEBRUARY, AND EVEN INTO THE WEEK 3-4 PERIOD, FAVORS AN ACTIVE PATTERN WITH ABOVE-NORMAL MONTHLY TOTAL PRECIPITATION AMOUNTS FOR MUCH OF THE CONUS. THE ODDS ARE GREATEST FOR CENTRAL AND SOUTHERN CALIFORNIA AND PARTS OF THE SOUTHWEST WHERE A FEW STRONG STORMS ARE LIKELY TO IMPACT THESE AREAS EARLY IN THE MONTH AND POTENTIALLY ONCE AGAIN NEAR THE MIDDLE OF THE MONTH. AN ACTIVE STORM TRACK ASSOCIATED WITH THE WEST-CENTRAL NORTH AMERICA TROUGH AND ITS VARIABILITY ALSO SUPPORTS HIGHER ODDS FOR ABOVE-NORMAL PRECIPITATION FOR PARTS OF THE LOWER MISSISSIPPI VALLEY, OHIO VALLEY AND GREAT LAKES. AS MENTIONED EARLIER, THE ANTICIPATED LARGE SCALE PATTERN FOR MUCH OF THE MONTH NEAR ALASKA ALSO FAVORS HIGHER ODDS OF ABOVE NORMAL PRECIPITATION FOR WESTERN ALASKA AS WELL. FOR SOME AREAS IN THE CENTRAL AND EASTERN CONUS PROBABILITIES ARE MORE MODEST AS THERE IS LIKELY TO BE CONSIDERABLE VARIABILITY IN THE STORM TRACK OVER THE COURSE OF MUCH OF FEBRUARY. RIDGING NEAR AND TO THE WEST OF WESTERN NORTH AMERICA FAVORS BELOW-NORMAL PRECIPITATION FOR AN AREA IN THE PACIFIC NORTHWEST AND ALASKA PANHANDLE FOR FEBRUARY. ******************************************************************************* ************* PREVIOUS MID-MONTH DISCUSSION (ROSENCRANS) ********************** ******************************************************************************* THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR FEBRUARY 2019 ARE BASED ON THE BACKGROUND ENSO STATE, POTENTIAL MJO ACTIVITY, AS WELL AS DYNAMICAL MODEL GUIDANCE. DYNAMICAL MODEL GUIDANCE AND STATISTICAL TOOLS THAT TYPICALLY SUPPORT THE WEEK 3-4 PERIOD, WHICH COVERS THE FIRST HALF THE MONTH, WERE ALSO USED. THE OBSERVED TEMPERATURE ANOMALY PATTERN DURING EARLY DECEMBER OVER THE CONUS EXHIBITED A DIPOLE STRUCTURE WITH COLDER THAN NORMAL EAST AND WARMER THAN NORMAL WEST. THE PATTERN THEN FLIPPED DURING LATER DECEMBER. JANUARY STARTED WITH A WARM EAST, BUT IS LIKELY TO FINISH WITH A COOLER THAN AVERAGE EAST AND WARMER THAN AVERAGE WESTERN CONUS. THE MJO LIKELY PLAYED A ROLE IN THESE NOTED SWITCHES, AND THE MJO IS PREDICTED TO REMAIN ACTIVE INTO FEBRUARY, THOUGH THE AMOUNT OF INFLUENCE CAN VARY MONTH TO MONTH DUE TO SEVERAL FACTORS. THE COLDER EASTERN CONUS ANTICIPATED IN LATER JANUARY IS CONSISTENT WITH A SUDDEN STRATOSPHERIC WARMING EVENT THAT TOOK PLACE IN EARLY JANUARY. ATTRIBUTION OF THE PATTERN IS STILL ONGOING. THE COLDER THAN NORMAL CONDITIONS ACROSS THE EASTERN CONUS ARE LIKELY TO CONTINUE FOR THE FIRST HALF OF FEBRUARY, WITH TEMPERATURES DURING THE LATTER HALF OF THE MONTH BEING LESS CERTAIN. DYNAMICAL MODELS DEPICTING THE FULL MONTH OUTLOOK INDICATE NEAR TO BELOW NORMAL CONDITIONS FOR MUCH OF THE EASTERN CONUS, WITH THE STRONGEST SIGNALS FOR COLD FROM THE GREAT LAKES TO TENNESSEE VALLEY AND TO THE SOUTHEAST. THE MULTIPLE LINEAR REGRESSION (MLR) TOOL THAT EXPLICITLY ACCOUNTS FOR THE MJO INFLUENCE INDICATES WARMER SIGNALS OVER THE EASTERN CONUS, SO THE PROBABILITIES IN THE OFFICIAL OUTLOOK ARE TEMPERED FROM THAT IN MANY OF THE DYNAMICAL MODELS, ESPECIALLY THOSE TOOLS GEARED TOWARD THE FIRST HALF THE MONTH. ACROSS THE WESTERN CONUS, A FORECAST FOR ABOVE NORMAL TEMPERATURES IS SUPPORTED BY DYNAMICAL MODEL PREDICTIONS AND TRENDS. THE MLR TOOL HAS A MUCH WEAKER SIGNAL ACROSS THE WESTERN CONUS, SO PLAYS LESS OF A ROLE. ACROSS ALASKA, TRENDS AND DYNAMICAL MODEL GUIDANCE FAVOR ABOVE NORMAL TEMPERATURES, THOUGH THE EXACT PLACEMENT OF THE AREAS WITH THE HIGHEST ODDS HAVE VARIED WITH RECENT MODEL RUNS. THE OFFICIAL OUTLOOK PLACES THE HIGHEST ODDS ACROSS SOUTHERN ALASKA AND THE ALASKA PANHANDLE AS THOSE LOCATIONS ARE LIKELY TO EXPERIENCE SOUTHERLY MEAN FLOW AT THE SURFACE. THERE IS SOME POTENTIAL FOR PERIODS OF COLD AIR TO SPILL INTO THE ALASKA PANHANDLE IF RIDGING OVER WESTERN CANADA SLIPS WESTWARD. THE PRECIPITATION OUTLOOK LARGELY REFLECTS DYNAMICAL MODEL GUIDANCE AND TRENDS, AS EXPRESSED IN BOTH THE SEASONAL OCN AND THE MLR TOOL. A MEAN STORM TRACK INTO SOUTHERN ALASKA FAVORS ABOVE NORMAL PRECIPITATION FOR SOUTHERN ALASKA AND THE ALASKA PANHANDLE, WITH THE MEAN STORM TRACK THEN DIPPING DOWN OVER THE NORTHERN GREAT PLAINS. ANOMALOUS RIDGING IS LIKELY TO PREVAIL ALONG THE WEST COAST DURING THE EARLY PORTIONS OF FEBRUARY, LIMITING THE POTENTIAL FOR LONG PERIODS OF WET WEATHER DURING A CLIMATOLOGICALLY WET PERIOD, SO BELOW NORMAL PRECIPITATION IS FAVORED FOR MUCH OF OREGON, CALIFORNIA, PORTIONS OF THE GREAT BASIN, AND PARTS OF THE SOUTHWEST. MEAN NORTHERLY FLOW, SUPPORTING THE COLDER THAN NORMAL TEMPERATURE OUTLOOK, ALSO FAVORS BELOW NORMAL PRECIPITATION FROM THE GREAT LAKES TO THE TENNESSEE VALLEY. ALONG THE GULF COAST AND EAST COAST, THE PLACEMENT OF THE MEAN FRONTAL ZONE COULD RESULT IN ABOVE NORMAL PRECIPITATION, BUT UNCERTAINTY IS TOO HIGH TO DEPICT A SIGNAL. FORECASTER: JON GOTTSCHALCK THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 COMPLETE DECADES AS THE CLIMATE REFERENCE PERIOD. THE PROBABILITY ANOMALIES FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS. THE NEXT MONTHLY OUTLOOK...FOR MAR ... WILL BE ISSUED ON THU FEB 21 2019 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$