Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260305_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)
=== ===== === ==== ==== === === === ====
Thu 03/05 12Z 0.07 2603  51  18   2 0.00
Thu 03/05 13Z 0.04 2702  50  19   2 0.00
Thu 03/05 14Z 0.02 0600  49  21   2 0.00
Thu 03/05 15Z 0.04 1303  51  22   2 0.00
Thu 03/05 16Z 0.11 1307  56  25   1 0.00
Thu 03/05 17Z 0.13 1309  60  25   1 0.00
Thu 03/05 18Z 0.13 1411  64  25   1 0.00
Thu 03/05 19Z 0.13 1412  70  28   0 0.00
Thu 03/05 20Z 0.15 1311  78  30   0 0.00
Thu 03/05 21Z 0.15 1312  83  32   0 0.00
Thu 03/05 22Z 0.11 1413  82  39   0 0.01
Thu 03/05 23Z 0.10 1413  80  49   1 0.01
Fri 03/06 00Z 0.13 1315  77  55   1 0.00
Fri 03/06 01Z 0.14 1316  79  62   1 0.00
Fri 03/06 02Z 0.14 1317  82  67   1 0.01
Fri 03/06 03Z 0.15 1318  85  70   1 0.01
Fri 03/06 04Z 0.14 1318  89  72   1 0.00
Fri 03/06 05Z 0.14 1317  91  72   1 0.01
Fri 03/06 06Z 0.13 1417  94  75   0 0.01
Fri 03/06 07Z 0.13 1417  96  74   0 0.01
Fri 03/06 08Z 0.13 1417  97  75   0 0.02
Fri 03/06 09Z 0.12 1417  96  73   0 0.01
Fri 03/06 10Z 0.12 1416  95  65   0 0.01
Fri 03/06 11Z 0.12 1416  95  56   0 0.00
Fri 03/06 12Z 0.11 1416  95  49   0 0.00
Fri 03/06 13Z 0.10 1415  95  43   0 0.00
Fri 03/06 14Z 0.08 1515  95  38   0 0.00
Fri 03/06 15Z 0.06 1515  95  34   0 0.00
Fri 03/06 16Z 0.04 1615  96  34   0 0.00
Fri 03/06 17Z 0.04 1614  96  31   0 0.00
Fri 03/06 18Z 0.04 1714  95  29   0 0.00
Fri 03/06 19Z 0.04 1714  94  27   0 0.00
Fri 03/06 20Z 0.04 1716  93  20   0 0.00
Fri 03/06 21Z 0.08 1817  94  33   0 0.00
Fri 03/06 22Z 0.12 1819  95  49   0 0.00
Fri 03/06 23Z 0.15 1821  95  59   0 0.00
Sat 03/07 00Z 0.18 1923  95  63   0 0.00
Sat 03/07 01Z 0.22 1925  95  52   0 0.00
Sat 03/07 02Z 0.25 1927  95  53   0 0.00
Sat 03/07 03Z 0.26 1928  95  48   1 0.00
Sat 03/07 04Z 0.24 1928  94  40   2 0.00
Sat 03/07 05Z 0.25 1929  94  18   3 0.00
Sat 03/07 06Z 0.28 2029  95  22   3 0.00
Sat 03/07 07Z 0.30 2029  95  45   4 0.01
Sat 03/07 08Z 0.33 2030  96  56   5 0.01
Sat 03/07 09Z 0.34 2032  97  81   5 0.02
Sat 03/07 10Z 0.39 2133  98  45   6 0.03
Sat 03/07 11Z 0.40 2132  97  84   7 0.04
Sat 03/07 12Z 0.41 2232  97  92   8 0.03
Sat 03/07 13Z 0.44 2231  97  92   8 0.02
Sat 03/07 14Z 0.45 2331  96  86   9 0.02
Sat 03/07 15Z 0.44 2330  95  80  10 0.01
Sat 03/07 16Z 0.46 2231  96  54  10 0.01
Sat 03/07 17Z 0.49 2233  95  35  10 0.01
Sat 03/07 19Z 0.54 2235  92  40  11 0.01
Sat 03/07 20Z 0.55 2335  91  70  12 0.00
Sat 03/07 21Z 0.55 2336  92  74  12 0.00
Sat 03/07 22Z 0.58 2238  94  59  12 0.01
Sat 03/07 23Z 0.67 2341  93  50  11 0.01

Run total areal avg QPF for the Central_Greens is: 0.35 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