Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1158 PM EDT Monday Sep 1 2014
Widely scattered showers will funnel into area overnight and
eventually focus over the southern County Warning Area late tonight into early
Tuesday as a secondary shortwave trough shifts through the area from
the southern stream. This activity will brush the I 94 terminals with
scattered...but somewhat persistent...activity around daybreak. To
the north...isolated rain showers will remain hit/miss into parts of the
overnight hours. Some patchy fog/stratus with IFR/MVFR conditions
will also be possible as low level moisture remains elevated. That
said...a general increase in middle/upper cloudiness with approaching
wave will limit this process to some extent. By middle/late morning
Tuesday...expect VFR conditions as drier air works into the area.
//Dtw threshold threats...
* low confidence that a thunderstorm will impact the terminal late
tonight into Tuesday morning.
* Low confidence in ceilings below 5000 feet late tonight into early
Previous discussion...issued 244 PM EDT Monday Sep 1 2014
Short term...this evening and tonight
18z special confirms the warmer column depicted by the rap and then
some. 900mb inversion is quite a bit more robust than depicted by
the guidance as is the 600mb cap. Thus, even the most tame
depictions of convection in the nwp are likely too aggressive and
concerns regarding capping noted in the morning update are
confirmed. Updrafts will struggle across most of the County Warning Area with the
exception of locations north of I-69 and especially west of US-23
where middle-level cooling and forcing will be maximized. With the line
already marching toward this area, expect that the abundance of
middle-level dry air and unidirectional flow above 1.5km will support
bowing segments carrying a low-end severe wind threat. In addition,
isolated tornado threat outlined in the earlier update remains in
tact. For remaining areas, expect nothing more than a gust to 40
miles per hour. In addition, backed off on probability of precipitation as earlier suspicions regarding
coverage potential still loom.
A weak cold front will sag through the area tonight. Frontal
inversion will promote expansion of stratus late tonight, but expect
that moisture will be too shallow and forcing too weak to support
any legitimate coverage or intensity of showers. With upper support
in the form of a shearing shortwave not scheduled to arrive until
Tuesday morning per 12z guidance, and mainly south of the area at
that, nothing more than a chance pop is warranted at this time.
Long term...Tuesday through next Monday
A cold front will be southeast of the County Warning Area to start out Tuesday
morning. However a middle level shortwave riding northeast along the
front will bring the chance for showers and thunderstorms to the
area Tuesday morning. After the shortwave tracks off to the
northeast significant drying will take place as a slug of 30 percent
relative humidity at 700 mb advects in from the west...ending rain
chances quickly early Tuesday afternoon. While there is still some
uncertainty regarding how far west the rain will fall given the push
of dry air advecting in...the latest suite of models has the drier
air pushing in a bit sooner than the 00z runs. Therefore will nudge
the forecast a bit drier Tuesday afternoon from the previous
forecast. Despite the passage of a cold front there isn't a large
push of cold air associated with it...meaning daytime highs are
expected to get around 80 Tuesday afternoon behind the front.
Ridging will keep the forecast dry through Wednesday as rebounding
heights allow daytime highs to get back into the lower 80s by
Moisture surge from the Gulf of Mexico commences on Thursday as a
low chance for convection exists within the warm sector of a
region-wide low pressure system. Best chance for thunderstorms
/possibly severe/ will be Friday as warm and moist airmass (85/70
T/td) is in place along with forecasted cape of 3000 j/kg. Bulk
shear increases to near 30 knots in the 1-6 km layer as well. These
ingredients will be in place as a ragged cold front crosses the
state. This brings a triple threat of severe weather with
wind...hail...and isolated tornadoes all possible
Showers and thunderstorms will track through the central Great Lakes
tonight as a cold front moves through Lake Huron and lower Michigan.
Some of these storms may be severe...mainly across the northern
portion of Lake Huron. High pressure will build into the region
behind this front on Tuesday...which will remain in control of the
weather through Thursday...providing favorable boating conditions.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).