A sharp, shallow cold front, bringing modified arctic air, will sweep across all of Deep South Texas and the Lower Rio Grande Valley overnight on the 27th and into the pre dawn hours of the 28th, changing springtime warmth and wind into ‘coat weather’ for the early morning commute and the school bus stop. The front will reach the Rio Grande Plains across to the northern edge of the King Ranch by mid evening on the 27th, than motor southward, crossing the mouth of the Rio Grande between midnight and 3 AM on the 28th. Temperatures will fall up to 20 degrees in two hours or less after the front passes, with readings generally between 65 and 70 prior to the front, and 45 to 50 two hours later. Wednesday morning will dawn brisk and overcast, along with areas of drizzle and patchy light rain, and temperatures ranging from the upper 30s to the mid 40s. Combined with north winds of 15 mph and gusty in the Lower Valley, wind chill values will likely range through the 30s, so persons venturing out between 3 and 9 AM should be prepared for the much colder weather. Wear several layers of light clothing to best insulate from the cold. By afternoon, partial clearing across the western Lower RGV through the Rio Grande Plains should allow temperatures to recover back into the 50s to around 60; a continuing low overcast from Weslaco to Brownsville may hold readings in the 40s for most of the day.
Casual boaters and fishers may be well advised to postpone trips later tonight into Wednesday, as the sharp front will rapidly increase sustained winds to near 30 knots, with gusts up to gale force, and seas will build quickly above 10 feet beyond 10 nautical miles out, perhaps briefly exceeding 12 feet beyond 20 nautical miles out during the early and mid morning hours of the 28th. Conditions should begin to improve late Wednesday and especially Wednesday night.
Conditions will improve somewhat on Thursday, the 29th, with a mix of clouds and some sunshine helping boost temperatures back into the 60s to near 70, along with lighter winds for both land and sea. Another front arrives overnight on the 29th, supplying a reinforcing shot of cool air but this time with abundant sunshine by the afternoon of Friday the 30th. After a chilly start with temperatures generally in the 40s, afternoon readings will recover into the 60s. Brisk northerly winds in the morning will diminish somewhat in the afternoon. However, the potential for winds still kicking up near 15 mph along with humidity dropping below 25 percent, and perhaps as low as 15 percent across the western Lower RGV, could elevate the potential for erratic spread of any wildfires that develop. Boaters will once again experience a rough go, especially early on the 30th, as northerly winds may gust above 25 knots and seas build to 8 feet or higher once again.
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