NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260425_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 04/25 18Z 0.46 0900  62  33   0 0.00
Sat 04/25 19Z 0.68 0801  61  32   0 0.00
Sat 04/25 20Z 0.72 1101  62  31   0 0.00
Sat 04/25 21Z 0.50 1101  63  30   1 0.00
Sat 04/25 22Z 0.33 0802  64  29   1 0.00
Sat 04/25 23Z 0.26 0802  65  30   0 0.00
Sun 04/26 00Z 0.21 0902  66  32   0 0.00
Sun 04/26 01Z 0.17 1102  66  33   0 0.00
Sun 04/26 02Z 0.16 0802  67  33   0 0.00
Sun 04/26 03Z 0.17 0702  67  32   0 0.00
Sun 04/26 04Z 0.18 0703  69  32   0 0.00
Sun 04/26 05Z 0.15 0602  69  34   0 0.00
Sun 04/26 06Z 0.09 0302  68  37   0 0.00
Sun 04/26 07Z 0.05 3502  68  37   0 0.00
Sun 04/26 08Z 0.07 0203  67  35   0 0.00
Sun 04/26 09Z 0.19 0405  65  31   0 0.00
Sun 04/26 10Z 0.15 0305  66  29   0 0.00
Sun 04/26 11Z 0.15 0305  65  30   0 0.00
Sun 04/26 12Z 0.17 0306  66  31   0 0.00
Sun 04/26 13Z 0.36 0306  67  30   0 0.00
Sun 04/26 14Z 1.27 0406  69  26   0 0.00
Sun 04/26 15Z 1.80 0305  71  24   0 0.00
Sun 04/26 16Z 0.87 0104  72  23   0 0.00
Sun 04/26 17Z 0.65 0005  72  21   1 0.00
Sun 04/26 18Z 0.45 0005  73  20   1 0.00
Sun 04/26 19Z 0.39 0005  74  16   1 0.00
Sun 04/26 20Z 0.50 0005  74  13   2 0.00
Sun 04/26 21Z 0.57 0105  73  12   2 0.00
Sun 04/26 22Z 0.47 0105  74  11   2 0.00
Sun 04/26 23Z 0.47 0305  73  10   2 0.00
Mon 04/27 00Z 0.38 0306  73  10   2 0.00
Mon 04/27 01Z 0.48 0306  72  11   2 0.00
Mon 04/27 02Z 0.55 0506  71  12   2 0.00
Mon 04/27 03Z 0.55 0506  71  13   2 0.00
Mon 04/27 04Z 0.57 0607  71  15   2 0.00
Mon 04/27 05Z 0.48 0706  71  17   2 0.00
Mon 04/27 06Z 0.36 0705  70  19   2 0.00
Mon 04/27 07Z 0.27 0704  69  22   2 0.00
Mon 04/27 08Z 0.17 0502  69  28   2 0.00
Mon 04/27 09Z 0.14 0303  70  35   2 0.00
Mon 04/27 10Z 0.21 0404  70  36   2 0.00
Mon 04/27 11Z 0.35 0606  70  36   2 0.00
Mon 04/27 12Z 0.34 0705  70  40   2 0.00
Mon 04/27 13Z 0.45 0705  70  40   2 0.00
Mon 04/27 14Z 1.02 0803  71  40   2 0.00
Mon 04/27 15Z 2.02 0904  71  38   2 0.00
Mon 04/27 16Z 1.73 1103  69  39   3 0.00
Mon 04/27 17Z 1.65 1203  66  38   4 0.00
Mon 04/27 18Z 2.61 1204  64  33   4 0.00
Mon 04/27 19Z 2.17 1304  61  31   5 0.00
Mon 04/27 20Z 1.81 1404  61  29   5 0.00
Mon 04/27 21Z 1.08 1504  61  28   5 0.00
Mon 04/27 22Z 0.45 1704  64  30   5 0.00
Mon 04/27 23Z 0.22 1605  64  27   5 0.00
Tue 04/28 00Z 0.08 1708  64  24   5 0.00
Tue 04/28 01Z 0.17 1910  64  23   5 0.00
Tue 04/28 02Z 0.11 1810  63  16   5 0.00
Tue 04/28 03Z 0.10 1810  61  12   5 0.00
Tue 04/28 04Z 0.06 1710  60  11   5 0.00
Tue 04/28 05Z 0.15 1612  56  10   5 0.00

Run total areal avg QPF for the greens is: 0.00 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