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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
403 am MDT Tuesday Jul 29 2014

Short term...(today through tonight )
issued at 403 am MDT Tuesday Jul 29 2014

Forecast this afternoon through tonight is rather complicated. There is a well
defined upper level disturbance over southwestern Utah which is moving north-northeast
with a secondary disturbance possibly over northestern Utah. Overall this
feature over northestern Utah may be the one that is supposed to move
slowly around the upper level high and into northern Colorado by tonight.
Meanwhile at the surface low pressure will be over southeastern Colorado as surface high pressure
builds into northern Colorado this evening.

Should see convection develop by midday in the mountains and then in and
near the foothills by early to middle afternoon and across the adjacent plains
by late afternoon. Precipitable water values are forecast to increase to
1.25 inches by late this afternoon with values possibly up to 1.5 inches
tonight over northestern Colorado if GFS is correct. Thus any storm will have
the potential to produce very heavy rain this afternoon through the early
evening hours.

For tonight if a widespread heavy rain event is going to develop will
have to get warm core rain processes to take over from middle evening through
the late night hours. There is some hint that a weak 700 mb
circulation will occur with the disturbance moving across tonight
and will combine with weak fnt moving into northestern Colorado to enhance Ely low
level flow in and near the higher terrain. So far the NAM...European model (ecmwf) and
the sref plumes are focusing on areas from Boulder County into Larimer
County while the GFS has a wound up 700 mb circulation center over
the eastern plains which focuses the heaviest rains away from the higher
terrain. Naturally if the warm rain processes get going after sunset
rainfall amounts over a 6 hour period can add up quickly as we saw
last September.

Long term...(wednesday through monday)
issued at 403 am MDT Tuesday Jul 29 2014

Looks like Wednesday is going to be the coolest day of the week
and maybe the wettest. The moist airmass is going to remain
anchored over the state with easterly flow from the surface up
to almost 600 mb. Quasi-geostrophic diagnostics from each of the
synoptic models show at least weak forcing for ascent over the
state through Monday afternoon. This should allow the upslope flow
to continue lifting the airmass...releasing the instability
through continued development of rain showers. Model soundings
from the NAM show a saturated and moist adiabatic
airmass...reminiscent of the shape seen during winter storms.
Precipitable water values are forecast to be at or above an inch
with an almost 8000 foot deep warm layer. All of the ingredients
for heavy rain look like they will be present. Will carry the
Flash Flood Watch through 6 PM Wednesday evening.

Through the rest of the forecast period...temperatures will remain
cooler than seasonal normals as the monsoonal flow keeps moisture
over Colorado. The upper flow pattern will be very complicated but
weak as the upper ridge remains over the southern rockies. Winds
aloft will be weak and northwesterly through Sunday and then may
switch to southerly on Monday as an upper trough pushes in from
the Great Basin. Monsoonal moisture will continue advecting over
the southwestern U.S. While a surface ridge over the Central
Plains sets up southerly low level flow...laden with Gulf
moisture...across eastern Colorado. Daytime heating will cause
airmass destabilization each afternoon...with slow moving
thunderstorms the result. Burn scars and areas that get rainfall
on consecutive days will be under the gun for flash flooding
problems.

&&

Aviation...(for the tafs through 12z Wednesday morning)
issued at 403 am MDT Tuesday Jul 29 2014

Will trend wind forecast towards hrrr through middle afternoon with winds becoming
more Ely by 18z. After 21z may see outflow boundaries from foothills
convection move across triggering scattered thunderstorms. If the Airport takes a
direct hit then could see heavy rainfall with low ceilings and
visibilties up to an hour as storms will be slow moving. For
tonight not sure how things are going to evolve. Could see a steady
rain event develop with a few embedded thunderstorms with MVFR/IFR ceilings
possible at times in areas of heavier rainfall.

&&

Hydrology...
issued at 403 am MDT Tuesday Jul 29 2014

The threat for flash flooding will increase this afternoon through
tonight. At this time it's still too early to tell where the
heaviest rains may focus. Overall rain amounts will average from
1 to 2 inches with 3 to 4 inches in a few locations. If the warm
rain processes kick in after sunset and continue overnight then a
more widespread heavy rain event could occur in some areas with
even higher rainfall totals. A Flash Flood Watch remains in
effect for the mountains...foothills and most of northeast
Colorado this afternoon through Wednesday.

&&

Bou watches/warnings/advisories...
Flash Flood Watch from 2 PM MDT this afternoon through Wednesday
afternoon for coz033>047-049.

&&

$$

Short term...rpk
long term...dankers
aviation...rpk
hydrology...rpk

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