Commentary on the forecast - Today and Tonight

High pressure will builds into the central Great Lakes during the course of the day and then slowly
shift east of the region late tonight. While this high will maintain relatively cool conditions
across the area as temperatures, lower to mid 50s, remain nearly 10F below average for daytime
maximum temperatures, it will also bringing clearing skies and easing winds.

So after a very cool start in the 30s, expect reasonable decent conditions by afternoon/early
evening in most locations. Portions of the Thumb will be the exception as northerly flow from cold
waters will limit high temperatures to the 40s in many cases.

With this high pressure drifting over the area this evening into the overnight hours, expect
temperatures to drop significantly. Will have to lower the going forecast, particularly over the
northeast quadrant of the forecast area as temperatures fall into the upper 20s to lower 30s with
such strong radiational cooling. An increase in high clouds associated with a developing elevated
warm front to the southwest of the area will limit cooling further south and west, so still expect
mid 30s over the western and southern periphery of the cwa.

.

Remaining Remarks on the forecast - Thursday through Tuesday

Big changes in the longwave pattern this weekend will result in a dreary week to come where
temperatures linger in the low 50s with potential for a lengthy wet period as well. Changes actually
begin the end of this week as a low amplitude upper level trough, with compact but strong closed
circulation, moves over the Great Lakes. This initial trough will shunt the ridge aloft off to the
east while the corresponding sfc low replaces high pressure that we will start the day Thursday
with. The longwave pattern takes its initial jog southward with this lead trough but it is merely
setting the stage for a much deeper closed system coming ashore southern California. This large
upper level trough will become cut off over the central Contiguous U.S. Monday which will result in
a slow drift through the midwest and Great Lakes through the week. An expansive cold pool with 850mb
temps down to -5C and 500mb temps approaching -20C will slowly work through the area during this
time which should keep temps below normal next week.

Back to the end of this week. Thursday we wills start off with high pressure over the area with the
mid level ridge axis crossing the area in the afternoon. This should hold off the approaching sfc
low and isotropically induced showers along the lifting warm front. Models are advertising a deep
dry layer up to 10Kft to start the day which will make it nearly impossible for any mid level
moisture to make it to the ground. They do advertise precipitable waters jumping from a third of an
inch to around an inch Thursday evening when the moisture pool ahead of the cold front works into
the area. For this will keep precip void of the area for most of Thursday before the band of showers
moves through during the evening/overnight. Southeasterly flow during most of the day will keep the
area on the cooler side with the potential for a brief PoP of warmer temps late in the afternoon if
winds veer a bit more to the sw right ahead of the front. Frontal timing will be key as will the
location of the sfc low center. The phasing of two lows will actually be occurring with the stronger
low passing through northern Michigan while a secondary low will pass just to our south, keeping the
better moisture and instability to our south as well. At this point will keep temps around 60. Will
also continue to leave thunder out of the forecast with the fropa due to lack of instability over
the area.

On Friday we will be dealing with dry slot working into the area behind the cold front while a
secondary cold front begins to drops south through lower Michigan. Will likely see a dry period with
dry air and subsidence right behind the front with chance type showers filling back in later. Height
will be climbing slightly as ridge draws near and westerly flow near the sfc will actually allow
some warm air advection to occur which will allow us to warm up a bit more into the 60. From here we
find ourselves on the cusp of warm and cold air and also wet or dry weather. This due to the fact
that the lead frontal band with the next system sets up somewhere through the Ohio Valley or lower
Michigan. Until we get some better resolution, will continue to highlight a gradient of low pops
across the area as we likely will not see 3-4 straight days of precip. Stay tuned for refinements.

. . posted at 345 AM EDT Wednesday April 23 2014


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