Help me decoding RMK section please
 

Guys, help me decoding the RMK section below.

RMK LTG DNST N-NE RAB26 CLD LYR FL040 VIS 3 BLO LYR VIS 7 ABV TOPS WND DATA ESTMD ALSTG/SLP ESTMD SHRA 3SE MOV E $=


Also, can you suggest me some good study resource or reference for unusual METAR/TAF decoding (for both FAA and ICAO)?

Thanks in advance.
;)

Lightening distant north-northeast. rain began 26 minutes after the last hour. cloud layer flight level 40 visibility 3 below layer 7 above tops of clouds. wind data estimated altimeter setting/sea level pressure estimated. rain shower 3 southeast moving east. maintenance is required on the automated observation system

The FAA does not set the standards for weather observations in the US, the National Weather Service does. The Federal Meteorological Handbook #1 is the guide for surface observations in the US and includes a chapter on remarks.