:: Octoberfest Rainouts
The never-ending parade of storm systems on a very active jet pattern continues after a quick break today. Octoberfests near and far have remained under the beer tents due to the rainfall...now bringing almost 3" of rain to Lakeville for the month, which is close to 2" over average. Where was this rain earlier this year? Farmers lament...lucky there is Octoberfest to keep spirits high.
Typically I write my own analysis and prognosis for the weather, but every few months or so I would just sound like a broken record as compared to one of the NWS offices' forecast discussions. So I just publish theirs instead. Today is one of those days. The detail and prognosis of both synoptic and mesoscale elements affecting our weather in the short term is great from the overnight cast of forecasters from Chanhassen. I will do a little deciphering and summary in the end:
FXUS63 KMPX 171056
AFDMPX
AREA FORECAST DISCUSSION...UPDATED TO ADD 12Z/AVIATION DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
550 AM CDT WED OCT 17 2007
.DISCUSSION...
UPPER TROUGH AXIS ORIENTED WEST TO EAST CONTINUES TO LIFT NORTHWARD
ACROSS NORTHERN MINNESOTA AND NORTHERN WISCONSIN. WEAK SFC TROUGH
ALSO CONTINUES TO LIFT NORTH. LAST OF SHOWER ACTIVITY HAS EXITED THE
NORTHERN CWA WITH PATCHY FOG REMAINING ALONG WITH PATCHY DRIZZLE.
DRIER LOW LEVEL AIR CONTINUES TO SURGE IN WHICH HAS HELPED
VISIBILITIES IMPROVE OVER THE LAST FEW HOURS. LOW CLOUD DECK ALSO
CONTINUES TO ADVANCE NORTHWARD WITH SMALL WEDGE OF CLEARING SKIES
ACROSS FAR SOUTHERN MINNESOTA WITH INCREASING MID LEVEL CLOUDS
FILLING IN CLOSE BEHIND AND REDEVELOPMENT OF LOW CLOUDS EXPECTED
THIS MORNING.
PRETTY IMPRESSIVE LOW PRESSURE TAKING SHAPE EARLY THIS MORNING AS
UPPER LEVEL LOW PRESSURE DIGS TOWARDS THE ROCKIES. 60 TO 80 METER
HEIGHT FALLS SHOWING UP IN 00Z UA ANALYSIS WITH 120 TO 140 METER
FALLS ANTICIPATED ACROSS THE CENTRAL PLAINS INTO THE MID MISSISSIPPI
RIVER VALLEY INTO THURSDAY AFTERNOON. SFC LOW NOW STARTING TO
INTENSIFY OVER FAR SOUTHEAST COLORADO/SOUTHWEST KANSAS. THIS FEATURE
WILL THEN GET KICKED NORTHEASTWARD AS UPPER TROUGH AXIS REACHES
IT THIS AFTERNOON AND RAPIDLY DEEPEN AS IT MOVES TOWARDS THE CWA. LOW
LEVEL FLOW IS RAPIDLY INCREASING ACROSS THE SOUTHERN PLAINS AHEAD
OF THE LOW WITH LOW CLOUDS ALREADY RACING NORTHWARD ACROSS KANSAS
WITH SOME SHOWER AND THUNDERSTORM DEVELOPMENT. WARM MOIST
TRANSPORT QUICKLY MOVES NORTHWARD TODAY PUTTING AND END TO THE
BRIEF DRY PERIOD THIS MORNING AND EARLY THIS AFTERNOON AS SHOWER
CHANCES BEGIN TO INCREASE. THE BIG INCREASE IN RAIN CHANCES COMES
THIS EVENING AS LOW LEVEL JET INTENSIFIES TO AROUND 50 KTS AND
POKES INTO SOUTHEAST MINNESOTA AND SOUTHWEST WISCONSIN. MOISTURE
TRANSPORT INCREASES WITH WARM LOW LEVEL WARM PUNCH AIDING INCREASE
IN LAYER DIFFERENTIAL TEMP ADVECTION AND THUS ASCENT. STRONG
CONVERGENCE ON THE NOSE OF THE LLJ /50-55 KTS CRASHING INTO 20-25
KTS/ OVER SOUTHERN AND EASTERN CWA FURTHER SUPPORTS ASCENT ALONG
WITH MID LEVEL FRONTOGENESIS SIGNALS INCREASING. IN
ADDITION...WEAK INSTABILITY SETS UP...ESPECIALLY AFTER
06Z...ACROSS THE SOUTHERN AND EASTERN CWA ALLOWING CONVECTION TO
ENTER THE PICTURE. ALL OF THESE FACTORS SUPPORT WIDESPREAD RAIN
WITH HEAVY AMOUNTS LOOKING MORE LIKELY. BANDS OF PRECIP WILL MOVE
TO THE NORTH INTO THURSDAY MORNING AS SFC LOW ENTERS SOUTHERN
MINNESOTA BY MIDDAY. THIS ALLOWS THE EASTERN CWA TO SEE A BIT OF A
BREAK IN THE RAIN BUT THE NORTHERN...CENTRAL... AND WESTERN AREAS
WILL CONTINUE TO SEE PRECIP AS DEFORMATION ZONE ORIENTS ITSELF FROM
SOUTHWEST TO NORTHEAST. THIS FEATURE THEN PIVOTS TO THE WEST
DURING THE AFTERNOON BEFORE BEING PULLED GRADUALLY NORTHEASTWARD
DURING THE EVENING AS LOW PULLS EAST INTO WISCONSIN. EXPECT
HIGHEST RAIN AMOUNTS TO RANGE FROM 1.5 TO 2 INCHES BY EARLY
FRIDAY. THE BULK OF THIS WILL FALL THIS EVENING AND TONIGHT. WILL
NEED TO WATCH RISES ON AREA RIVERS...NAMELY ACROSS SOUTH CENTRAL
MINNESOTA WHERE IT HAS BEEN VERY WET AS OF LATE. THERE IS STILL
DISAGREEMENT BETWEEN THE NAM AND GFS WITH HOW FAST THE LOW PULLS
EAST...WITH THE NAM BEING SLOWER. THIS LOWERS CONFIDENCE IN FRIDAY
POP FORECAST BUT AM LEANING TOWARDS A SLOWER DEPARTURE. STRONG
NORTHWEST WINDS WILL BUILD IN BEHIND THE LOW THURSDAY NIGHT AND
FRIDAY...ESPECIALLY ACROSS THE WESTERN CWA. SPEEDS OF 20 TO 30 MPH
WITH HIGHER GUSTS WILL BE POSSIBLE.
HIGH PRESSURE AT THE SURFACE AND ALOFT CRESTS OVER THE REGION
SATURDAY ALLOWING FOR A DRY DAY. NEXT CHALLENGE WILL BE ANOTHER
UPPER LOW WHICH DIGS INTO THE SOUTHWEST U.S. EARLY SUNDAY SPAWNING
ANOTHER SFC LOW DEVELOPMENT. MODELS CONTINUE TO HAVE CONSISTENCY
TROUBLES WITH THIS SYSTEM BUT PRECIP CHANCES WILL BE RETURNING
SUNDAY. TEMPERATURES SATURDAY WILL WARM INTO THE LOW TO MID 60S
WITH SOME SUNSHINE RETURNING. ..MDB..
Quick translation and summary: Low pressure systems previous to today floated away from the jet stream (cutting off from the dynamics of the upper atmosphere) and became entrenched over our area. The last of those cold upper lows has drifted into Ontario, and behind it the upper jet has ridged enough to allow a brief reprise of dry air and a few peaks of sun today. By this afternoon, another low pressure system -- this one being actively supported by the jet stream -- will push northwestbound from Kansas. Ahead of it, the low altitude winds which will bring moisture and warmth from the Gulf of Mexico will collide and interact with upper altitude winds that is giving "spin" and drive to the cyclonic system. As the whole thing moves towards us, shower and thunderstorm activity will increase.
Get ready for more rain!