Thursday, May 29, 2014
The Category 4 hurricane southwest of the Baja peninsula that was Amanda became the strongest May eastern Pacific hurricane on record Sunday morning as peak winds approached that of a Category 5 hurricane. Much of the current moisture has been drawn northward from the remains of that hurricane, and will persist over our area through Saturday.
The moisture will keep the night unseasonably warm, and there will be enough daytime heating in spite of the cloud cover to force afternoon storms through Saturday. Additionally, weak and hard-to-time waves will enhance storms on Friday, leading to that day being the wettest of the period. The warm rain will accelerate the melting of the upper elevation snowpack leading to further rising of the rivers through the weekend.
Waves staying north of us, the first from the northwest late in the weekend and then a series from the southwest early in the week, will draw dry air into the region by Sunday, noticeably decreasing the chance of afternoon storms and lowering nighttime temperatures. The summery weather looks to last through most of next week before a weak wave may bring a threat of showers near the end of the workweek, though they would likely be limited to the typical afternoon variety.
Thursday, May 22, 2014
A large upper level low cut off from the mean westerly flow currently sits over central to southern California and will affect our weather for the Memorial Day weekend. Atmospheric moisture will increase each day in first southwest and then southerly flow as the low is forecast to lumber across Arizona and New Mexico through the long weekend. Additionally, a wave in the westerly flow to our north will interact with this low Saturday and more strongly Sunday bringing progressively stronger and wetter conditions to our region through Sunday night.
As is usual during the late spring and summer months, showers should increase as we approach the warmest part of the day, and then decrease as night falls, though the interaction with the wave to the north will keep activity going longer than normal Saturday and Sunday nights.
This interaction should move the low to our east by Monday and lead to noticeably drier and warmer weather. However we will still be susceptible to afternoon showers Monday as the cool air in the mid and upper levels left behind by the storm keeps the atmosphere unstable.
Conditions will be warmer and drier on Tuesday, though we may still see some passing afternoon showers. By early Wednesday, we are completely under the influence of a dry and summery warm airmass that looks to hang around through the remainder of the workweek.
Thursday, May 15, 2014
A couple of more days of unsettled early spring-like weather will be in store for tomorrow and and early Saturday as the huge storm that impacted us over the weekend finally trudges far enough east of us to allow the return of seasonable weather. Two shortwaves timed for Friday afternoon and Saturday morning will keep showers going, more so on Friday afternoon than Saturday.
By late Saturday or early Sunday, a rapidly building ridge will bring much warmer temperatures and drier air for the end of the weekend and extending into the beginning of the workweek. However, by midweek, another forecast storm approaching form the Pacific northwest splits, with models struggling with how much energy will be partitioned between the northern and southern branches.
Most models keep most of the storm to our southwest, with some of the storm moving quickly across the northern Rockies. Current forecasts skirt a cool front through our region sometime on Wednesday leading to an increased chance of showers. This will be followed later in the week with warm and possibly wet weather as the storm to our southwest moves over us late in the week or early in the Memorial Day weekend.
Thursday, May 8, 2014
An expanding ridge over Hudson Bay has pushed its eponymous vortex westward into the Canadian Plains, providing a source of cold air that has fed into today’s passing storm and produced non-accumulating snow showers in the Yampa valley this morning. This pool of cold air will again be drawn into the next storm currently making landfall in the Pacific northwest as it approaches our area, creating moderate to heavy precipitation by Sunday.
Until then, showers will continue today and increase towards sunset as the limited daytime heating continues to destabilize the atmosphere. A quick moving and low amplitude ridge should clear the showers later tonight and tomorrow morning before waves of energy ejecting out of the incoming storm allow showers to redevelop Friday afternoon.
Saturday may also start out relatively nice as breezy southwest flow moves over our area ahead of the advancing storm to our west. The cold front is predicted to move through our area Saturday afternoon or evening and will eventually bring significant precipitation to all of Colorado by Sunday. Any rain in the valley should turn to snow during the night as precipitation ramps up and continues at moderate to heavy levels during the day Sunday. Accumulations on the hill will likely be over a foot by Monday morning, especially at the higher elevations, though accumulations in the valley will be limited by warm ground temperatures and any small warming seen during daylight hours.
Monday will start quite chilly before additional waves of energy and cool air from the Hudson Bay vortex will regenerate much lighter showers by Monday afternoon. Earlier model runs had warming and drying by midweek, but as happened many times this year, we will be susceptible to continued showers and cool air surges during the workweek as waves rotate around the west side of the pesky Hudson Bay vortex.
Thursday, May 1, 2014
A ridge currently centered along the west coast is moving east towards our area and will bring warm and dry conditions that will persist into the new workweek. Several waves spinning around the Hudson Bay vortex will stay well to our north and east tomorrow and Saturday, but flatten the ridge, keeping temperatures around seasonal levels. There may be enough moisture and instability for afternoon clouds and a few thunderstorms, though this activity will be isolated. The ridge regains some of its lost amplitude by Sunday after these waves pass leading to unseasonably warm temperatures that will last at least through Monday.
However, this warm and dry weather will end around midweek when another wave forecast to make landfall in the Pacific northwest on Sunday begins to influence our area. The European ECWMF now agrees with the American GFS model with the early evolution of the storm, leading to warm and windy conditions ahead of this storm for Tuesday. Both models now have cold air from the Hudson Bay vortex entering the storm on Tuesday, but the American GFS continues to pour cold air into the backside of the storm leading to another prolonged cool and wet period from Wednesday through at least part of next weekend. The European ECMWF currently does not show this additional energy entering the storm and keeps it fast moving and through the area by Thursday.
Confidence that a storm will be over our area around midweek is high, but the details are uncertain. My inclination is to believe the cool and wet pattern advertised by the GFS as that model seems to be better handling the Hudson Bay vortex and its interaction with energy entering the west coast from the Pacific.