NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260522_1200
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 05/22 12Z 0.18 0308  61   3   0 0.00
Fri 05/22 13Z 0.21 0308  58   3   0 0.00
Fri 05/22 14Z 0.31 0307  57   3   0 0.00
Fri 05/22 15Z 1.27 0406  58   4   0 0.00
Fri 05/22 16Z 1.68 0404  56   6   1 0.00
Fri 05/22 17Z 0.97 0302  54   9   2 0.00
Fri 05/22 18Z 0.52 0101  54  13   3 0.00
Fri 05/22 19Z 0.35 0001  56  16   3 0.00
Fri 05/22 20Z 0.33 0002  57  18   4 0.00
Fri 05/22 21Z 0.35 0102  58  21   4 0.00
Fri 05/22 22Z 0.24 0102  59  22   4 0.00
Fri 05/22 23Z 0.19 0203  58  23   4 0.00
Sat 05/23 00Z 0.22 0303  56  23   4 0.00
Sat 05/23 01Z 0.26 0503  53  24   4 0.00
Sat 05/23 02Z 0.25 0504  50  24   4 0.00
Sat 05/23 03Z 0.23 0604  48  25   4 0.00
Sat 05/23 04Z 0.27 0705  47  26   4 0.00
Sat 05/23 05Z 0.31 0806  48  27   4 0.00
Sat 05/23 06Z 0.36 0808  47  24   4 0.00
Sat 05/23 07Z 0.45 0809  42  20   4 0.00
Sat 05/23 08Z 0.50 0811  39  16   4 0.00
Sat 05/23 09Z 0.54 1012  42  11   4 0.00
Sat 05/23 10Z 0.55 1114  45   7   4 0.00
Sat 05/23 11Z 0.55 1116  45   5   4 0.00
Sat 05/23 12Z 0.53 1217  44   4   4 0.00
Sat 05/23 13Z 0.50 1218  47   3   3 0.00
Sat 05/23 14Z 0.46 1217  49   3   4 0.00
Sat 05/23 15Z 0.45 1216  51   4   4 0.00
Sat 05/23 16Z 0.47 1215  55   4   4 0.00
Sat 05/23 17Z 0.48 1315  57   4   3 0.00
Sat 05/23 18Z 0.50 1315  58   3   4 0.00
Sat 05/23 19Z 0.45 1415  60   3   3 0.00
Sat 05/23 20Z 0.41 1415  62   3   3 0.00
Sat 05/23 21Z 0.36 1416  62   3   4 0.00
Sat 05/23 22Z 0.32 1418  61   2   4 0.00
Sat 05/23 23Z 0.34 1420  57   2   4 0.00
Sun 05/24 00Z 0.33 1423  52   3   4 0.00
Sun 05/24 01Z 0.35 1425  49   8   4 0.00
Sun 05/24 02Z 0.34 1426  48  19   4 0.00
Sun 05/24 03Z 0.30 1426  51  37   4 0.00
Sun 05/24 04Z 0.28 1427  53  58   4 0.00
Sun 05/24 05Z 0.26 1529  53  87   5 0.00
Sun 05/24 06Z 0.23 1529  57  94   5 0.00
Sun 05/24 07Z 0.26 1430  66  98   5 0.01
Sun 05/24 08Z 0.33 1432  73  99   5 0.03
Sun 05/24 09Z 0.37 1435  75  99   4 0.02
Sun 05/24 10Z 0.35 1436  80  99   4 0.03
Sun 05/24 11Z 0.33 1438  87  99   4 0.07
Sun 05/24 12Z 0.29 1439  90  99   5 0.08
Sun 05/24 13Z 0.26 1439  90  99   5 0.07
Sun 05/24 14Z 0.20 1539  93  99   5 0.09
Sun 05/24 15Z 0.16 1539  95  96   5 0.12
Sun 05/24 16Z 0.10 1638  96  98   5 0.13
Sun 05/24 17Z 0.07 1636  97  98   5 0.14
Sun 05/24 18Z 0.05 1635  97  98   5 0.10
Sun 05/24 19Z 0.05 1735  97  96   6 0.06
Sun 05/24 20Z 0.05 1735  97  84   6 0.04
Sun 05/24 21Z 0.05 1736  97  78   7 0.03
Sun 05/24 22Z 0.05 1735  97  69   7 0.03
Sun 05/24 23Z 0.06 1733  97  52   8 0.03

Run total areal avg QPF for the Central_Greens is: 1.08 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