NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260514_0000
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)
=== ===== === ==== ==== === === === ====
Thu 05/14 00Z 0.18 1927  88  66   5 0.00
Thu 05/14 01Z 0.19 1929  79  57   6 0.00
Thu 05/14 02Z 0.18 1929  77  54   6 0.00
Thu 05/14 03Z 0.15 1928  78  58   6 0.00
Thu 05/14 04Z 0.12 1826  77  60   6 0.00
Thu 05/14 05Z 0.15 1926  78  67   6 0.00
Thu 05/14 06Z 0.16 1927  80  72   6 0.00
Thu 05/14 07Z 0.13 1925  86  77   6 0.00
Thu 05/14 08Z 0.05 1824  91  86   5 0.01
Thu 05/14 09Z 0.04 1724  95  85   5 0.04
Thu 05/14 10Z 0.04 1725  97  92   5 0.03
Thu 05/14 11Z 0.05 1726  97  95   5 0.04
Thu 05/14 12Z 0.05 1825  98  97   5 0.05
Thu 05/14 13Z 0.08 1821  98  94   5 0.05
Thu 05/14 14Z 0.08 1817  99  90   5 0.04
Thu 05/14 15Z 0.10 1614  99  91   5 0.05
Thu 05/14 16Z 0.20 1515  99  95   5 0.09
Thu 05/14 17Z 0.34 1419  99  96   5 0.16
Thu 05/14 18Z 0.45 1318  98  98   5 0.17
Thu 05/14 19Z 0.56 1220  98  98   4 0.17
Thu 05/14 20Z 0.59 1218  99  98   4 0.14
Thu 05/14 21Z 0.52 1114  98  98   4 0.13
Thu 05/14 22Z 0.49 1113  97  97   5 0.11
Thu 05/14 23Z 0.53 0914  97  96   5 0.09
Fri 05/15 00Z 0.52 0914  97  94   4 0.08
Fri 05/15 01Z 0.62 0917  97  98   4 0.10
Fri 05/15 02Z 0.65 0919  96  96   4 0.11
Fri 05/15 03Z 0.69 0920  95  96   4 0.12
Fri 05/15 04Z 0.74 1024  95  96   4 0.09
Fri 05/15 05Z 0.84 1028  94  94   4 0.05
Fri 05/15 06Z 0.84 1029  90  91   4 0.03
Fri 05/15 07Z 0.83 1029  89  91   3 0.02
Fri 05/15 08Z 0.79 1027  91  91   3 0.02
Fri 05/15 09Z 0.77 1026  92  85   3 0.01
Fri 05/15 10Z 0.72 1023  90  92   3 0.01
Fri 05/15 11Z 0.70 1021  90  81   3 0.02
Fri 05/15 12Z 0.66 0919  88  75   3 0.01
Fri 05/15 13Z 0.67 0918  86  71   3 0.01
Fri 05/15 14Z 0.69 0917  85  77   3 0.01
Fri 05/15 15Z 0.73 0915  88  77   3 0.00
Fri 05/15 16Z 0.98 0811  92  72   3 0.00
Fri 05/15 17Z 0.98 0809  91  73   3 0.00
Fri 05/15 18Z 0.90 0908  90  74   3 0.01
Fri 05/15 19Z 0.58 0906  90  76   3 0.01
Fri 05/15 20Z 0.44 0905  89  76   3 0.01
Fri 05/15 21Z 0.26 1105  89  76   4 0.01
Fri 05/15 22Z 0.16 1403  89  77   4 0.02
Fri 05/15 23Z 0.16 1602  88  80   4 0.02
Sat 05/16 00Z 0.15 2201  87  76   4 0.01
Sat 05/16 01Z 0.14 2601  83  67   4 0.00
Sat 05/16 02Z 0.14 2702  78  55   5 0.00
Sat 05/16 03Z 0.13 2502  73  47   5 0.00
Sat 05/16 04Z 0.19 2306  77  44   4 0.00
Sat 05/16 05Z 0.30 2409  81  43   4 0.00
Sat 05/16 06Z 0.34 2410  82  39   4 0.00
Sat 05/16 07Z 0.38 2512  86  34   4 0.00
Sat 05/16 08Z 0.39 2513  89  32   4 0.00
Sat 05/16 09Z 0.41 2513  87  30   4 0.00
Sat 05/16 10Z 0.49 2516  88  39   4 0.00
Sat 05/16 11Z 0.54 2518  86  38   4 0.00

Run total areal avg QPF for the greens is: 2.15 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