FLC OF DC10 ENCOUNTERS TSTMS AND IS UNABLE TO LAND AT DEST ARPT. WHEN ATTEMPTING TO GO TO THEIR ALTERNATE WX AGAIN IMPACTS THE ARRS. THEY DECLARE LOW FUEL AND DIVERT TO DCA.

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A TSTM MOVED RAPIDLY ACROSS THE FIELD AT BWI AS WE WERE ON FINAL APCH. WE COULD CLRLY SEE THE RWY; BUT AT 100 FT; VISIBILITY WENT TO ZERO WITH HVY RAIN AND WINDSHEAR. FO EXECUTED A MISSED APCH AND ATC VECTORED US FOR ANOTHER APCH. TWR RPTED WINDSHEARS OF 50 KTS AND CAPT DECIDED TO GO TO IAD; OUR ALTERNATE. PART WAY THERE; IAD APCH SAID THEY WERE NOT ACCEPTING APCHS DUE TO HVY TSTM. AT THIS POINT; SINCE WX WAS BTWN US AND OUR OTHER ALTERNATE; RIC; AND SINCE FUEL WAS DOWN TO 17000 LBS; AND SINCE DCA WAS IN THE CLR; WE DIVERTED TO DCA. APCH AND LNDG WAS NORMAL AT DCA. DURING FLT FROM ORD-BWI; ATC GAVE US A RERTE QUITE FAR S; AND EXTENSIVE VECTORING; INCLUDING CONSIDERABLE TIME WBOUND BURNING CONSIDERABLE FUEL. ACARS TERMINAL WX SHOWED NO PROBS AT BWI; IAD; DCA OR RIC. WHEN WE GOT INTO THE WASHINGTON AREA; THE TSTMS WE COULD SEE LOOKED SMALL AND DID NOT PAINT MUCH ON RADAR. TFC LANDED AT BWI APPROX 4-5 MINS AHEAD OF US. THE TSTMS INTENSIFIED RAPIDLY AND MOVED RAPIDLY TO ARRIVE WHEN WE DID -- THUS THE DIVERSION. I'M NOT SURE WHAT COULD HAVE PREVENTED THIS; FORECASTS DID NOT CALL FOR TSTMS ON OUR ARR; THOUGH THEY WERE KNOWN TO BE IN THE AREA. HAD WE KNOWN EARLIER HOW FAST THEY WERE MOVING; WE WOULD HAVE BEEN BETTER PREPARED AND COULD HAVE CHOSEN A BETTER ALTERNATE. UNTIL WX FORECASTING AND DISSEMINATION IS BETTER; WE MAY HAVE TO EXPECT A DEV LIKE THIS. EVEN THE ATIS AT BWI DID NOT INDICATE A PROB BEFORE OUR APCH.