Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260315_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)
=== ===== === ==== ==== === === === ====
Sun 03/15 12Z 0.07 3207  48  50  -8 0.00
Sun 03/15 13Z 0.03 3405  41  78  -7 0.00
Sun 03/15 14Z 0.02 3301  43  90  -7 0.00
Sun 03/15 15Z 0.02 1602  46  97  -7 0.00
Sun 03/15 16Z 0.02 1607  46  97  -6 0.00
Sun 03/15 17Z 0.05 1611  47  98  -6 0.00
Sun 03/15 18Z 0.03 1615  60  98  -6 0.00
Sun 03/15 19Z 0.04 1619  71  98  -6 0.00
Sun 03/15 20Z 0.08 1624  59  97  -5 0.01
Sun 03/15 21Z 0.10 1629  48  93  -4 0.00
Sun 03/15 22Z 0.05 1631  46  89  -3 0.00
Sun 03/15 23Z 0.09 1734  49  95  -3 0.00
Mon 03/16 00Z 0.13 1738  53  92  -2 0.00
Mon 03/16 01Z 0.17 1840  51  84  -1 0.00
Mon 03/16 02Z 0.20 1843  45  72   0 0.00
Mon 03/16 03Z 0.19 1845  52  64   1 0.00
Mon 03/16 04Z 0.18 1846  62  51   2 0.00
Mon 03/16 05Z 0.16 1848  79  76   3 0.00
Mon 03/16 07Z 0.09 1750  94  34   4 0.01
Mon 03/16 08Z 0.05 1749  93  59   5 0.01
Mon 03/16 09Z 0.05 1649  91  90   6 0.01
Mon 03/16 10Z 0.08 1650  94  97   7 0.02
Mon 03/16 11Z 0.08 1651  94  92   8 0.03
Mon 03/16 12Z 0.05 1650  96  98   8 0.04
Mon 03/16 13Z 0.13 1746  97  61   8 0.09
Mon 03/16 14Z 0.24 1844  97  46   9 0.05
Mon 03/16 15Z 0.33 1945  97  19   9 0.02
Mon 03/16 16Z 0.40 1945  97  12  10 0.02
Mon 03/16 17Z 0.47 1943  95  30  10 0.01
Mon 03/16 18Z 0.54 1942  95  26  10 0.01
Mon 03/16 19Z 0.52 1938  96  25  10 0.00
Mon 03/16 20Z 0.46 1938  96  27  10 0.00
Mon 03/16 21Z 0.41 1844  96  74  10 0.00
Mon 03/16 22Z 0.46 1847  95  92   9 0.02
Mon 03/16 23Z 0.28 1845  96  95   9 0.03
Tue 03/17 00Z 0.21 1745  96  84  10 0.07
Tue 03/17 01Z 0.25 1845  97  85   9 0.04
Tue 03/17 02Z 0.18 1743  97  84   9 0.03
Tue 03/17 03Z 0.15 1743  96  93   9 0.03
Tue 03/17 04Z 0.14 1743  96  89   9 0.04
Tue 03/17 05Z 0.04 1744  96  96   9 0.04
Tue 03/17 06Z 0.05 1743  96  95  10 0.04
Tue 03/17 07Z 0.50 1933  99  98   7 0.09
Tue 03/17 08Z 0.68 2429  94  97  -1 0.16
Tue 03/17 09Z 1.66 2433  96  29  -7 0.06
Tue 03/17 10Z 2.68 2532  96   3  -9 0.03
Tue 03/17 11Z 14.14 2535  77  11 -12 0.03
Tue 03/17 12Z 10.48 2437  72  15 -14 0.01
Tue 03/17 13Z 20.49 2436  80  22 -16 0.00
Tue 03/17 14Z 21.75 2435  69  15 -17 0.00
Tue 03/17 15Z 21.49 2435  66  17 -17 0.00
Tue 03/17 16Z 22.98 2434  70  19 -16 0.00
Tue 03/17 17Z 21.70 2431  69  22 -16 0.00
Tue 03/17 18Z 20.51 2530  71  28 -16 0.00
Tue 03/17 19Z 20.65 2530  73  30 -16 0.00
Tue 03/17 20Z 19.62 2530  76  39 -16 0.00
Tue 03/17 21Z 18.90 2530  76  44 -16 0.00
Tue 03/17 22Z 17.01 2631  79  46 -16 0.00
Tue 03/17 23Z 12.80 2632  84  46 -17 0.00

Run total areal avg QPF for the Central_Greens is: 1.05 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