NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260424_0000
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 04/24 00Z 0.39 3321  44  30   1 0.00
Fri 04/24 01Z 0.35 3322  44  26   0 0.00
Fri 04/24 02Z 0.26 3320  45  10   0 0.00
Fri 04/24 03Z 0.18 3417  48   4   0 0.00
Fri 04/24 04Z 0.14 3514  56   4  -1 0.00
Fri 04/24 05Z 0.13 0013  62   4  -2 0.00
Fri 04/24 06Z 0.10 0012  65   5  -3 0.00
Fri 04/24 07Z 0.05 3512  63   7  -4 0.00
Fri 04/24 08Z 0.06 3412  62   7  -5 0.00
Fri 04/24 09Z 0.09 3415  61   5  -5 0.00
Fri 04/24 10Z 0.06 3417  59   4  -6 0.00
Fri 04/24 11Z 0.04 3417  58   5  -5 0.00
Fri 04/24 12Z 0.03 3516  59  13  -5 0.00
Fri 04/24 13Z 0.03 3514  59  31  -5 0.00
Fri 04/24 14Z 0.06 3512  59  39  -5 0.00
Fri 04/24 15Z 0.46 3410  60  37  -5 0.00
Fri 04/24 16Z 0.98 3310  61  32  -4 0.00
Fri 04/24 17Z 1.41 3310  61  22  -4 0.00
Fri 04/24 18Z 0.99 3310  60  13  -3 0.00
Fri 04/24 19Z 1.21 3310  59  13  -3 0.00
Fri 04/24 20Z 0.78 3411  58  14  -2 0.00
Fri 04/24 21Z 0.30 3412  60  15  -2 0.00
Fri 04/24 22Z 0.52 3511  63  14  -2 0.00
Fri 04/24 23Z 0.53 0012  68  12  -2 0.00
Sat 04/25 00Z 0.45 0114  71  11  -3 0.00
Sat 04/25 01Z 0.62 0216  73  13  -3 0.00
Sat 04/25 02Z 0.69 0316  73  16  -4 0.00
Sat 04/25 03Z 0.74 0417  72  17  -4 0.00
Sat 04/25 04Z 0.66 0518  68  15  -3 0.00
Sat 04/25 05Z 0.52 0515  64  10  -4 0.00
Sat 04/25 06Z 0.38 0710  63   5  -3 0.00
Sat 04/25 07Z 0.28 0908  64   3  -3 0.00
Sat 04/25 08Z 0.23 1008  64   3  -3 0.00
Sat 04/25 09Z 0.13 1308  64   3  -3 0.00
Sat 04/25 10Z 0.12 1308  66   2  -3 0.00
Sat 04/25 11Z 0.13 1308  69   3  -2 0.00
Sat 04/25 12Z 0.13 1208  69   3  -2 0.00
Sat 04/25 13Z 0.13 1207  70   2  -2 0.00
Sat 04/25 14Z 0.13 1306  70   2  -3 0.00
Sat 04/25 15Z 0.25 1305  67   3  -2 0.00
Sat 04/25 16Z 0.63 1205  63   3  -2 0.00
Sat 04/25 17Z 1.06 1204  61   3  -1 0.00
Sat 04/25 18Z 1.29 1204  61   3  -1 0.00
Sat 04/25 19Z 1.06 1303  60   3  -1 0.00
Sat 04/25 20Z 1.28 1203  59   3   0 0.00
Sat 04/25 21Z 1.23 1104  58   3   0 0.00
Sat 04/25 22Z 0.45 1104  57   4   0 0.00
Sat 04/25 23Z 0.33 1105  56   5   0 0.00
Sun 04/26 00Z 0.31 1106  56   6   0 0.00
Sun 04/26 01Z 0.37 1108  57   8   0 0.00
Sun 04/26 02Z 0.38 1109  58   8   0 0.00
Sun 04/26 03Z 0.28 1208  57   7   0 0.00
Sun 04/26 04Z 0.22 1307  57   9   0 0.00
Sun 04/26 05Z 0.24 1208  57   9   0 0.00
Sun 04/26 06Z 0.26 1209  57   7   0 0.00
Sun 04/26 07Z 0.34 1110  55   7   0 0.00
Sun 04/26 08Z 0.36 1110  54   6   0 0.00
Sun 04/26 09Z 0.37 1210  57   8   0 0.00
Sun 04/26 10Z 0.35 1210  58  12  -1 0.00
Sun 04/26 11Z 0.42 1210  62  28  -1 0.00

Run total areal avg QPF for the Central_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