Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Junction Colorado
1055 am MDT Thursday Jul 31 2014
issued at 753 am MDT Thursday Jul 31 2014
Updated morning grids for next couple hours as some patchy fog is
occurring along the I-70 corridor near Avon and in the northern
valleys near Craig...Hayden...and Meeker with some low ceilings.
This is likely due to saturated ground from rain that occurred
yesterday for areas along and north of I-70. Also updated for
cloud cover in the northern and central Colorado areas. Expecting
fog to burn off by 15z and low ceilings to lift as surface heating
takes place. Forecast still on track for development of afternoon
thunderstorms over the higher terrain with best coverage south of
I-70. Some storms may drift off higher terrain late afternoon into
some southern and central Colorado valleys.
Short term...(today through friday)
issued at 417 am MDT Thursday Jul 31 2014
Morning low temperatures flirting with records as Grand Junction
has a rather mild July 31st record low of 58 set in 1909 and
sitting at 60 as of 4 am this morning. Still a few hours of
cooling to go...so a new record could be hit. After the cool start
to the day...afternoon maximum temperatures expected to remain a good 10
degrees below normal for most locations.
Focus of convection shifts to our southern zones today with activity
firing over the San Juan Mountains by late morning and then
spreading over into the valleys this afternoon and evening. Plenty
of moisture still in place with precipitable water values over an
inch. So expect locally heavy rainfall and potential for more mud
slides near steep terrain. Convection will be a bit more isolated
across our northern zones with subtle drying behind weak wave that
passed last evening.
Due to a somewhat drier air mass...the afternoon's convection will
diminish by late in the evening. Any lingering nocturnal activity
limited to the southeast corner of the forecast area where
precipitable water values will still be nearly an inch.
An embedded disturbance traveling from the central California coast will
pass over the northern half of the forecast area on Friday. This
will provide an additional boost to the daytime instability.
However the more unstable north will also be the driest portion of
the forecast area. Precipitable water there drops to almost half
an inch...but stays closer to an inch along our southern edge. So
while the north is in a better position for the disturbance...the
south has the better moisture. Therefore expect we will again see
showers and thunderstorms develop during the afternoon...mainly
over the higher terrain. Heavy rain will not be as likely due to
the less available moisture. And do not expect the rain production
to be quite as efficient as it has been the past couple of days.
Also the flow will be from the west-northwest at around 15 kts in
the south...adequate to keep the storms moving along. The flow
will be a little lighter up north...but also that area will be
Low temperatures will be near normal...with highs staying a little
below normal for this time of year.
Long term...(friday night through wednesday)
issued at 417 am MDT Thursday Jul 31 2014
Moisture continues to diminish on Saturday with precipitable
water dropping below half an inch over a large section of the
forecast area. Therefore look for a down turn in the afternoon
shower and thunderstorm activity. With less clouds and
showers...temperatures will climb to around normal.
Ridge axis slides back into the plains by early next week opening
The Gates back up for another surge of deeper monsoonal moisture.
Models hinting at a stronger wave lifting north across The Four
Corners late Sunday...with a second stronger wave following late
Monday night and Tuesday. This second wave looks to sweep the
deeper moisture out into the plains by the middle of next week
with ridging rebuilding to our west. This would bring drier northwesterly
flow into the forecast area by Wednesday. Temperatures expected to remain
near seasonal norms through the later periods of the extended.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1055 am MDT Thursday Jul 31 2014
Scattered showers and thunderstorms expected to develop just
before 18z over the higher terrain with some drifting into the
valleys after 21z. Areas south of I-70 are expected to see
greater coverage than north of I-70. Expect heavy rain and gusty
winds to 40 miles per hour to be the primary threats with storms...with
mountain obscurations in any storms and heavy rain. Storms will
linger until 06z before coming to an end.