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"If summer were a Broadway show, this week, the role of \"July\" would be played by an unusual understudy: \"January.\" At least, as far as the weather pattern is concerned.\nConsider how weird the weather will be in Canada and the U.S. this week.\nSee also: Cold Snap in July: Will the Real Polar Vortex Please Stand Up?\nFirst, there's the cold.\nA huge southward dip in the jet stream, which is causing air to move from the Arctic into the U.S., is already bringing record cold temperatures, with overnight lows in the 40-degree range Fahrenheit, and daytime highs barely nudging past 60 degrees Fahrenheit in parts of the Midwest on Monday and Tuesday.\nDuluth, Minnesota, was just 57 degrees Fahrenheit at noon on Monday, with a chilly north wind of 20 miles per hour. In Chicago, Illinois, the high temperature is not likely to make it much past 70 degrees Fahrenheit at a time of year when they are frequently in the mid-90s.\n\nMorning low temperature forecast for Tuesday, July 15, 2014 according to the GFS model.Image:  WeatherBell AnalyticsAccording to the National Weather Service (NWS), in Minneapolis-St. Paul, Minnesota, a record will likely be set for the coldest high temperature ever recorded on July 14. In fact, the temperature will be more typical of early October.\nMinnesota meteorologist Paul Douglas said the cold weather is a reminder that extreme weather has become the norm in recent years.\n\nThe terminology we've been using is all wrong. Global warming suggests everyone warms up, simultaneously. Climate change? Our climate has always changed, although this time we're the ones stepping on the accelerator,\" he said on his Minneapolis Star Tribune blog.\nClimate volatility is a better descriptor. From a record warm 2012 to last winter's Polar Vortex. From \"flash drought\" last summer to June 2014, the wettest month in Minnesota history. That's what we're seeing in the data and on the maps.\nExhibit A: today, perfectly average for early October. A few instability showers pop up this afternoon; highs stuck in the low to mid 60s - probably the coolest July 14 on record for MSP. Meanwhile highs will soar to 90F near the Arctic Circle, topping 100F over British Columbia.\nExtremes right out of some fictional, hard-to-believe Hollywood blockbuster.\n\nKansas City, Missouri, Chicago and Omaha, Nebraska, may break cold temperature records on Tuesday. On Wednesday, at least two dozen cities will threaten daily record lows.\nThe cold front that marks the dividing line between the fall-like air mass to the north and the typically hot and humid July air to the south is sparking two days of severe weather from the Ohio Valley to the East Coast and will then make it all the way to the Gulf Coast before stalling out midweek.\nIt is extremely rare, although not unheard of, for a cold front to sweep that far south in July, and relief from the humidity, even for a few days, is atypical in states like Arkansas, Mississippi, Georgia, and North Carolina at this time of year either. Yet that is what is about to happen.\nThe cool weather, with highs from 10 to 25 degrees Fahrenheit below average, won't be long-lasting like it was in January, however. (Nor will it actually feel like January. Give July a little credit, will ya?) Temperatures should begin to rebound by Thursday in most areas.\nOr, to put that in technical terms while screaming, \"THE HIGH-AMPLITUDE MERIDIONAL EPISODE OVER NORTH AMERICA IS FORECAST TO REACH ITS APOGEE EARLY IN THE MEDIUM RANGE,\" the NWS said in a forecast discussion on Monday (their style is ALL-CAPS).\nThen, there's the rain.\nThe good news about this weather pattern \u2014 and yes, it really is related to what is meteorologically known as the polar vortex (more on that in a moment) \u2014 is that once the cold front stalls out in the South, ripples of energy will move along it, sparking several days of wet weather in parched areas of Texas, Oklahoma and New Mexico.\nWichita Falls has had its driest 45-month period on record, and is forecast to receive anywhere from two to four inches of rain this week, according to Victor Murphy, an NWS meteorologist in Dallas. Murphy told Mashable that the rains could have the biggest benefits in the Wichita Falls and Dallas-Ft. Worth areas, which have missed out on much of the rainfall that has fallen across the state so far this spring and summer.\nSince Oct. 1, 2010, Wichita Falls has had 66.35 inches of rain, compared to the normal for the period, which is about 110 inches, Murphy says. \"...They have \u201Cmissed\u201D out on about 1.5 years worth of precipitation in the past 3.75 years.\"\n\nProjected 5-day rainfall totals, showing heavy rains falling along a cold front.Image:  NOAA HPCDallas, for example, has had its driest year since 1972, and the city has grown dramatically since then, adding to water demands. The reservoirs that serve Dallas are at their lowest levels since 1990, Murphy said. In Wichita Falls, reservoir levels are at 23.4% of capacity, which is the lowest on record.\nIn the South, Murphy says, \u201CThe benefits of this anomalously strong cold front should outweigh any negative implications.\u201D\nMurphy said the combination of a cold front moving all the way to Houston and New Orleans, plus a series of weak storm systems moving along it, is \"really unusual for this time of year.\u201D Typically, any widespread heavy rainfall in July or August comes from landfalling hurricanes somewhere in the Gulf of Mexico, not cold fronts accompanied by powerful jet stream winds.\nAlso, there's the heat.\nThe flip side to the jet stream dive in the Midwest and East is a \"ridge\" or bulge of high pressure in the West, which is leading to much warmer than average conditions in the Pacific Northwest and Western Canada. Along with this heat comes high fire danger, with \" target=\"_blank\"&gt;fires already breaking out in Washington and British Columbia.\nA heat wave in Seattle is expected to continue into midweek, which could keep the city on course to have its warmest or second-warmest July on record. Triple-digit heat is also roasting parts of interior Washington state to eastern Oregon and California's parched Central Valley.\nThere are signs that more heat could build into interior Canada next week, extending from the Mexican border all the way to Hudson Bay. This, too, could lead to dangerous wildfire risks.\n\nGiant trough the story this week, major ridge the story next week. It is flip flop season, after all. pic.twitter.com/dvccUDuKO6\n\u2014 Eric Fisher (@ericfisher) July 14, 2014\n\n\u00A0\nThis weird weather comes courtesy of the polar vortex.\nMeteorologists disagree about the precise definition of the polar vortex and whether the cool air that has invaded the U.S. is part of this phenomenon, since it manifests itself differently during the summer than during the winter. However, enough evidence exists to conclude that this invasion of fall-like air during what should actually be the beginning of the \"dog days\" of summer is connected to the polar vortex.\n\nComputer model animation showing the source region of the unusually cool air mass that entered the Midwest U.S.Image:  WeatherBell.com via Capital Weather Gang blogFor one thing, the air mass at the mid-and-upper levels is coming from the Arctic, as evident in computer model simulations and observations.\n\nModel showing the simulated trajectory of an air mass moving into the Midwest.Image:  NOAA via Eric Holthaus/Slate.comFor another, it is part of the circumpolar vortex at the top of the troposphere, which is related to the polar vortex that also exists in the next atmospheric layer up, known as the stratosphere.\n\nThe tropopause vortex that moves into CONUS next week has residence time N. of arctic circle, per theta(PV) @nws pic.twitter.com/Av4t1Z9Z9G\n\u2014 Greg Postel (@GregPostel) July 11, 2014\n\n\u00A0\nThe Washington Post's Capital Weather Gang blog has more on why this event has clear links to the polar vortex.\nHave something to add to this story? 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