Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260304_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)
=== ===== === ==== ==== === === === ====
Wed 03/04 18Z 0.23 2809  75   1   0 0.00
Wed 03/04 19Z 0.28 2611  72   2   0 0.00
Wed 03/04 21Z 0.49 2617  61   7   0 0.00
Wed 03/04 22Z 0.50 2717  57  12   1 0.00
Wed 03/04 23Z 0.47 2716  56  17   1 0.00
Thu 03/05 00Z 0.44 2716  52  22   1 0.00
Thu 03/05 01Z 0.40 2715  48  25   2 0.00
Thu 03/05 02Z 0.39 2715  44  27   2 0.00
Thu 03/05 03Z 0.41 2716  44  28   2 0.00
Thu 03/05 05Z 0.37 2815  47  27   1 0.00
Thu 03/05 07Z 0.27 2812  52  16   1 0.00
Thu 03/05 08Z 0.24 2811  56  15   1 0.00
Thu 03/05 09Z 0.21 2809  60  15   1 0.00
Thu 03/05 10Z 0.18 2809  62  12   1 0.00
Thu 03/05 11Z 0.11 2906  64  11   1 0.00
Thu 03/05 12Z 0.05 3104  67  11   1 0.00
Thu 03/05 13Z 0.02 3302  69  11   1 0.00
Thu 03/05 14Z 0.03 1000  70  14   1 0.00
Thu 03/05 15Z 0.06 1104  71  15   1 0.00
Thu 03/05 16Z 0.08 1206  75  17   1 0.00
Thu 03/05 17Z 0.09 1308  77  18   0 0.00
Thu 03/05 18Z 0.10 1410  81  20   0 0.00
Thu 03/05 19Z 0.09 1412  84  22   0 0.00
Thu 03/05 20Z 0.09 1412  81  23   0 0.00
Thu 03/05 21Z 0.08 1412  76  24   0 0.00
Thu 03/05 22Z 0.08 1412  71  24   1 0.01
Thu 03/05 23Z 0.09 1412  70  25   1 0.01
Fri 03/06 00Z 0.11 1414  69  32   1 0.01
Fri 03/06 02Z 0.11 1417  75  53   1 0.01
Fri 03/06 03Z 0.12 1418  80  61   0 0.01
Fri 03/06 04Z 0.11 1417  85  69   0 0.01
Fri 03/06 05Z 0.11 1417  90  77   0 0.00
Fri 03/06 06Z 0.12 1419  93  88   0 0.00
Fri 03/06 07Z 0.10 1519  95  93   0 0.00
Fri 03/06 08Z 0.09 1518  96  97   0 0.00
Fri 03/06 09Z 0.08 1518  96  99   0 0.02
Fri 03/06 10Z 0.09 1518  95  97   0 0.03
Fri 03/06 11Z 0.10 1519  94  91   0 0.03
Fri 03/06 12Z 0.09 1519  95  85   0 0.03
Fri 03/06 13Z 0.10 1520  94  73   0 0.03
Fri 03/06 14Z 0.08 1520  94  66   0 0.02
Fri 03/06 15Z 0.08 1520  94  53   0 0.00
Fri 03/06 16Z 0.07 1519  94  49   0 0.00
Fri 03/06 18Z 0.03 1619  94  51   0 0.00
Fri 03/06 19Z 0.03 1718  95  58   0 0.00
Fri 03/06 20Z 0.03 1718  95  62   0 0.00
Fri 03/06 21Z 0.05 1721  94  55   0 0.00
Fri 03/06 22Z 0.07 1722  95  45   1 0.00
Fri 03/06 23Z 0.10 1823  96  40   1 0.00
Sat 03/07 00Z 0.13 1824  96  50   2 0.00
Sat 03/07 01Z 0.14 1825  97  39   2 0.00
Sat 03/07 02Z 0.16 1827  97  47   3 0.00
Sat 03/07 03Z 0.18 1929  97  39   3 0.00
Sat 03/07 04Z 0.19 1930  97  16   3 0.00
Sat 03/07 05Z 0.23 1930  97  29   3 0.01

Run total areal avg QPF for the Central_Greens is: 0.23 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