Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
541 am EST Thursday Dec 25 2014
Scattered -shra will stream east through areas between I 69 and I 94
early in the forecast before ending after 14z or so. While IFR ceilings
will be possible early...expect MVFR ceilings in general...which will
lift with time and break out this afternoon into this evening. VFR
conditions should be common tonight as high pressure builds into
area and lower stratus/strato-cu scatters out. Southwest winds will
remain elevated today with gusts reaching 20-25 knots into the middle
afternoon. A decoupling boundary layer will lead to south-southwest winds under
10 knots tonight
For dtw...expect generally MVFR ceilings with a sprinkle or two early
this morning. MVFR conditions will most likely hold into afternoon
but ceilings will rise and become more broken in nature...before scattering
out entirely this evening into tonight. Wind gusts to near 25 knots
from 230 degrees can be expected into the 21z-23z time frame.
//Dtw threshold probabilities...
* high in ceilings below 5000 feet through 23z...low in the 23z-03z
Previous discussion...issued 250 am EST Thursday Dec 25 2014
Short term...today and tonight
Remaining light rain and snow showers tracking through area with
weak wave that is wrapping around main low pressure circulation to
the north will end early this evening...leaving mostly cloudy skies
into much of the day. Even with a decided lack of sunshine...cold
air advection in the wake of overnight storm system will end by 18z
with warm air advection already in place prior to 00z. This will
lead to relatively mild temperatures and will edge highs closer to
guidance readings by adding 1 or 2 degrees area-wide to the going
forecast. West to southwest flow will persist within decent pressure
gradient through today...aiding in keeping temperatures relatively
mild for late December.
Weak shortwave ridge will build into area already tonight as upper
trough evolves over the southern rockies and southern High Plains.
This feature...along with surface high pressure should lead to some
break in the clouds by evening. Winds will also slacken considerably
with the loss of boundary layer mixing...so temperatures should be
able to drop off fairly well tonight...even in the moderating air
mass. Will leave low temperatures...upper 20s to lower 30s...as is
for this forecast package.
Long term...Friday through next Wednesday
Friday will have building heights as a shortwave ridge builds over
the eastern U.S. Moisture profile suggest that Southeast Michigan should
at least start with partly sunny skies. There will be some hi
altocumulus and cirrus ahead of the shearing shortwave that will be
ejecting from the inter mountain system. By late Friday...a good
surge of 850-700 mb moisture will also ensure that mostly cloudy
skies return by the evening. With some sun...went closer to the
warmer mav/GFS guidance numbers.
As the moisture advection continues ahead of that sheared out
shortwave with deep and strong SW flow...the chance of showers
increase on Friday night especially for the northern part of the
forecast area. Given the moisture surge that eventually gets into
the boundary layer later Friday night...added patchy drizzle for
late Friday night and early Saturday. Expect a Friday evening low
before temperatures are steady or even slowly rise during the
overnight hours with the good SW flow. The entire forecast area
should not have any issues staying above freezing and thus keeping
the precipitation liquid.
Finally by Saturday...that sheared out shortwave moves through lower
Michigan accompanied by the a cold frontal passage late in the day.
There really is not much going for Saturday other than that weak
shortwave...cold front and some upper divergence as we get into the
right rear entrance region of a 140 knots jet by late in the day. For
the most part will keep the probability of precipitation in the chance category. Guidance
numbers for Saturday were close and do not see any reason to differ.
Saturday should have a familiar feel with plenty of clouds...a damp
feel but mild for December.
By Saturday evening the cold front passes through the region and
should bring in enough cold air that any residual showers mix with
and change to snow showers before ending. Again with the lack of
any forcing...probability of precipitation will continue to be in the chance category.
The remainder of the forecast remains very quite. A general
lowering of The Heights with more of a troughing northwest flow will
bring in colder temperatures for Sunday through Wednesday...nothing
extreme just closer to average for the end of December.
Low pressure just northeast of Lake Huron will continue to pull away
today. As it does...gales will remain for portions of Lake Huron
early in the day and then diminish. By late in the day today...a
ridge of high pressure will build over the central and eastern
lakes. After the passage of this weak ridge...moderate southwest
winds up to around 20 kts will develop for Friday and Friday night
ahead of a cold front. That cold front will pass through late
Saturday and Saturday night. Behind the cold front will be another
round of moderate winds from the northwest.
Lake Huron...Gale Warning until 7 am EST this morning for lhz363-462.
Small Craft Advisory until 4 PM EST this afternoon for lhz421-441.
Gale Warning until 11 am EST this morning for lhz361-362.
Lake St Clair...none.
Michigan waters of Lake Erie...low water advisory until noon EST today for lez444.
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at www.Weather.Gov/Detroit (all lower case).