(12/13/12) (12/10/12) (12/10/12) (12/9/12) (12/6/12) (12/6/12) (12/4/12) (12/3/12) (11/28/12) (11/28/12)
COD Student Forecast
Posted: (12/13/12) at 9:59am
Short-Term Discussion:
The brutal cold that has the majority of Canada firmly in its grasp, has led to low temps nearing the -40° mark as far south as ctrl Manitoba/nrn Ontario/wrn Hudson Bay. This arctic air mass has been contained primarily to Canada thanks to a split jet structure that has taken shape across N America. 500MB heights identify a polar jet weaving across SCtrl Canada, while WV imagery clearly shows the presence of a strong trop jet between 15°N/30°N from sw of Hawaii through the Nrn Gulf of Mex before turning up the E coast. To no surprise, the current pattern has yielded additional precip along the west coast. This batch of precip, however, has pushed further south and inland, spreading from Srn CA through Srn ID. The recent Swd migration of this precip is due to a digging trough nearly paralleling the W coast while the main energy of the trough has lingered on the backside, associated with a stern positive tilt.

Closer to home...throughout the post weekend period, weve seen slightly warmer than normal temps, allowing OHare airport to reach a 15th consecutive day at or above the daily avg, despite a weakly amplified trough in place across the region. Over the next few days, the trough will abate as it moves Ewd with a strong high in place from S TX to Nrn ME. This will allow a pressure gradient that is set up to our WSW to penetrate further into the CWA, waning slightly Thurs as a shortwave passes to our N, before strengthening again Fri, ahead of an approaching Low. The E/W associated gradient will induce warmer air to advect Nwd, with increasingly anomalous temps through the weekend.

Model guidance is in good agreement that the trough, currently digging S off the W coast, will nearly cut off from the Nrn jet, with a low developing ahead of the trough. The main jet streak will move into the left entrance region of the trough and round the corner while strengthening to 110kts. The strengthening jet streak will tap into the moisture brought into the region by the trop jet, causing heavy precip across AZ/NM, before the jet streak ejects into the TX/OK panhandle region. This setup will help to organize the low as the system progresses NEwd this weekend. Prior to its arrival in the CWA, this setup shows decent potential for severe in TX/OK on Fri, with 60°F dew points advecting into Ctrl TX,,, This would be quite an exciting setup in a more unstable atmos.

Back home, Fri/Sat, winds will increase, gusting up to 30kts Fri night into sat. Moderate precip will sprawl across the CWA as the low moves just to the NW across IA/MN/WI. The NAM/GFS/ECMWF thoroughly agree we will be far into the warm sector of this system, with temps fri/sat approaching 50°F, making the threat for accumulating snow nearly impossible here. CAA will occur on the backside of the low, however, will not force temps to get unseasonably cold, in fact I wont be surprised if we prolong our days above avg streak into next week.
5-Day Forecast
Tonight: High: 49°F/Low:35°F Abundant sunshine with only a few high level clouds as a result of a short wave to our north. Highs throughout the area will flirt with 50°F, enabling the area to reach a 16th straight day at or above normal temps, the longest such streak since a 43 day above average stretch ended Aug. 9th. Despite clear skies, tonight’s lows will stay slightly elevated as a result of a well mixed atmos.
Friday: High:52°F/Low:37°F 50°F will become even more likely tomorrow, providing we’re able to evade the clouds associated with the approaching warm front. SSW winds tomorrow will be weaker early in the afternoon, before they ramp back up tomorrow night. Again, lack of a decoupled atmos along with increasing clouds will keep temps up throughout the overnight hours.
Saturday: High:45°F/Low:39°F Saturday will quickly turn into a gloomy/rainy day as a low moves to our NW. Guidance precip totals range from roughly .5” to 1.5” with the mean near .8”. If we receive over .51” of precip, this will be the wettest weekend we’ve seen since Oct. 12th-14th. 10-20 kt winds will be a factor as well, however, will turn calmer, backing out of the SSE as the day progresses.
Sunday: High:44°F/Low:34°F Sunday will open with overcast skies but only isolated drizzle remaining from Saturday’s passing low. Winds will be much calmer, yet temps will stay nearly steady in the mid 40s throughout the day, before dipping into the mid 30s overnight.
Monday: High:38°F/Low:30°F Multiple layers of clouds may allow a peak of sunshine Monday afternoon, but expect mostly overcast skies, which will limit sunshine and therefore keep daytime heating to a minimum. Monday will see more seasonable temps, still slightly above average. Winds will range between 5-10kts.

Long-Term Discussion:
The UL trough associated with Saturdays system will only remain in the area through midday Tuesday at the latest, as weak ridging begins to build across the ctrl US. LR guidance prog waves to continually crash into the W coast, with approximately 5-7 waves making landfall over the next 10 days. As the long waves are weakened by the imminent landfall, this persistence will allow for continuous short waves/UL troughs to move across our area followed by periods of slight ridging. This pattern of imbedded short waves throughout a more broad, zonal pattern, should allow temps to fluctuate from near avg to slightly above avg for the foreseeable future. An interesting component, evident in LR model guidance, is the presence of the aforementioned trop jet that fluctuates in strength, yet overall, persistently brings rarely tapped moisture into the SW US. This should cause the periodic waves moving across the Rockies and Desert SW to intensify slightly, with the aid of higher UL heights S of the trop jet. Models seem to like the idea of a more amplified trough forming late in the period across the Wrn US. Due to both the added moisture and tightened PG, but model guidance may be having a tough time dealing with this complex situation. Therefore, I wouldn’t be shocked to see one or more of these waves dump a substantial amount of precip somewhere throughout the Ern two-thirds of the nation. However, with arctic air still unavailable throughout most of the conus, unfortunately, I believe snow is fairly unlikely across the CWA anytime before the week of xmas.
Forecaster(s): John Wills -(Meteorology Major)