Unfortunately, rain tends to destroy pollen.
If there is sufficient rainwater the pollen grains will absorb the water and they can burst. Whether any pollen is still alive (viable) may depend on how much rain has fallen. It also will depend on whether the rain started before the pollen actually finished its "ripening" process - whether the anthers had actually opened and the pollen grains had dried out and fluffed-up. If the rain had started before then, and it stops and the sun warms and dries everything out then the anthers may open and the pollen will most likely be good because it will complete its "ripening" process after the rain or in a dry period between rainfalls.
On some days, even after long rainfalls, it is sometimes possible to find a flower or two that opened in such a way that the rain drops did not manage to wet the anthers and harm the pollen. Sometimes that is because one or more other flowers (or flower buds) prevented the flower from opening properly. You may then find "good" looking pollen (dry & fluffy not lumped together in what may seem to be hard clumps).
