NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260710_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 07/10 18Z 0.25 3508  88  69  13 0.00
Fri 07/10 19Z 0.18 3410  87  70  13 0.02
Fri 07/10 20Z 0.16 3412  84  65  13 0.03
Fri 07/10 21Z 0.05 3511  78  51  14 0.01
Fri 07/10 22Z 0.09 3510  74  34  14 0.00
Fri 07/10 23Z 0.05 3510  73  27  14 0.00
Sat 07/11 00Z 0.07 3510  72  24  13 0.00
Sat 07/11 01Z 0.07 3510  71  21  13 0.00
Sat 07/11 02Z 0.08 3511  73  27  13 0.00
Sat 07/11 03Z 0.07 3510  75  22  12 0.00
Sat 07/11 04Z 0.09 3511  72  19  12 0.00
Sat 07/11 05Z 0.18 0011  69  30  12 0.00
Sat 07/11 06Z 0.21 0110  67  44  12 0.00
Sat 07/11 07Z 0.20 0109  66  54  11 0.00
Sat 07/11 08Z 0.20 0108  66  61  11 0.00
Sat 07/11 09Z 0.17 0107  66  70  11 0.00
Sat 07/11 10Z 0.15 0107  66  67  11 0.00
Sat 07/11 11Z 0.11 0107  66  70  11 0.00
Sat 07/11 12Z 0.16 0107  67  63  11 0.00
Sat 07/11 13Z 0.14 0106  68  37  11 0.00
Sat 07/11 14Z 0.23 3505  71  27  10 0.00
Sat 07/11 15Z 0.32 3505  72  23  11 0.00
Sat 07/11 16Z 0.31 3405  74  25  11 0.00
Sat 07/11 17Z 0.36 3505  76  30  11 0.01
Sat 07/11 18Z 0.62 0006  76  21  11 0.01
Sat 07/11 19Z 0.58 3506  74  16  11 0.00
Sat 07/11 20Z 0.52 3507  74  19  11 0.00
Sat 07/11 21Z 0.63 0008  73  12  11 0.00
Sat 07/11 22Z 0.57 0009  73   9  11 0.00
Sat 07/11 23Z 0.56 0110  73   8  11 0.00
Sun 07/12 00Z 0.54 0111  73   8  11 0.00
Sun 07/12 01Z 0.52 0213  73   8  10 0.00
Sun 07/12 02Z 0.61 0314  74   9  10 0.00
Sun 07/12 03Z 0.66 0314  74  12  10 0.00
Sun 07/12 04Z 0.66 0314  73  13  10 0.00
Sun 07/12 05Z 0.61 0413  72  16  10 0.00
Sun 07/12 06Z 0.60 0413  72  18  10 0.00
Sun 07/12 07Z 0.56 0413  71  18  10 0.00
Sun 07/12 08Z 0.51 0412  72  18  10 0.00
Sun 07/12 09Z 0.47 0411  75  17   9 0.00
Sun 07/12 10Z 0.41 0409  76  13   9 0.00
Sun 07/12 11Z 0.33 0408  76  10   9 0.00
Sun 07/12 12Z 0.27 0407  76   9   9 0.00
Sun 07/12 13Z 0.24 0306  76   8   9 0.00
Sun 07/12 14Z 0.27 0204  77   7  10 0.00
Sun 07/12 15Z 0.16 3503  79   7  10 0.00
Sun 07/12 16Z 0.11 3402  79   7  10 0.00
Sun 07/12 17Z 0.16 3403  79   6  11 0.00
Sun 07/12 18Z 0.15 3303  79   6  11 0.00
Sun 07/12 19Z 0.27 3202  78   7  11 0.00
Sun 07/12 20Z 0.41 3104  75  11  12 0.00
Sun 07/12 21Z 0.40 3004  69  11  12 0.00
Sun 07/12 22Z 0.29 3004  61   7  12 0.00
Sun 07/12 23Z 0.20 3004  57   6  12 0.00
Mon 07/13 00Z 0.23 2804  57   6  12 0.00
Mon 07/13 01Z 0.34 2705  63   5  12 0.00
Mon 07/13 02Z 0.42 2706  69   6  12 0.00
Mon 07/13 03Z 0.53 2506  73   6  11 0.00
Mon 07/13 04Z 0.73 2408  74   7  11 0.00
Mon 07/13 05Z 0.85 2411  76   9  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1