Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260728_1800
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)
=== ===== === ==== ==== === === === ====
Tue 07/28 18Z 0.19 1610  91  78  15 0.00
Tue 07/28 19Z 0.39 1612  89  78  15 0.05
Tue 07/28 20Z 0.35 1613  88  79  15 0.11
Tue 07/28 21Z 0.33 1615  88  79  15 0.10
Tue 07/28 22Z 0.19 1719  92  85  15 0.16
Tue 07/28 23Z 0.11 1722  93  88  14 0.18
Wed 07/29 00Z 0.08 1724  93  89  14 0.10
Wed 07/29 01Z 0.09 1821  92  83  14 0.01
Wed 07/29 02Z 0.12 1721  95  83  14 0.01
Wed 07/29 03Z 0.18 1625  96  86  14 0.02
Wed 07/29 04Z 0.19 1629  96  85  14 0.03
Wed 07/29 05Z 0.15 1729  95  87  14 0.02
Wed 07/29 06Z 0.12 1728  95  90  14 0.03
Wed 07/29 07Z 0.17 1627  94  85  14 0.02
Wed 07/29 08Z 0.23 1628  94  88  14 0.01
Wed 07/29 09Z 0.30 1530  94  88  14 0.01
Wed 07/29 10Z 0.34 1530  95  88  14 0.02
Wed 07/29 11Z 0.41 1531  96  90  14 0.04
Wed 07/29 12Z 0.51 1431  95  90  13 0.07
Wed 07/29 13Z 0.64 1431  93  92  13 0.11
Wed 07/29 14Z 0.80 1334  94  93  13 0.16
Wed 07/29 15Z 0.90 1334  96  94  13 0.13
Wed 07/29 16Z 1.15 1335  96  91  13 0.13
Wed 07/29 17Z 0.70 1434  96  91  14 0.12
Wed 07/29 18Z 0.64 1433  97  94  13 0.15
Wed 07/29 19Z 0.54 1534  97  90  14 0.23
Wed 07/29 20Z 0.54 1429  97  92  14 0.12
Wed 07/29 21Z 0.48 1426  97  93  14 0.09
Wed 07/29 22Z 0.49 1426  96  94  14 0.06
Wed 07/29 23Z 0.53 1326  96  94  14 0.07
Thu 07/30 00Z 0.56 1326  95  94  14 0.12
Thu 07/30 01Z 0.53 1326  95  89  13 0.12
Thu 07/30 02Z 0.53 1227  96  88  13 0.05
Thu 07/30 03Z 0.53 1329  96  90  13 0.05
Thu 07/30 04Z 0.50 1329  96  93  13 0.08
Thu 07/30 05Z 0.50 1328  96  91  13 0.09
Thu 07/30 06Z 0.47 1327  94  88  14 0.04
Thu 07/30 07Z 0.42 1326  94  91  14 0.02
Thu 07/30 08Z 0.40 1325  95  93  14 0.03
Thu 07/30 09Z 0.43 1326  95  92  13 0.07
Thu 07/30 10Z 0.45 1225  94  93  13 0.04
Thu 07/30 11Z 0.47 1225  94  92  13 0.02
Thu 07/30 12Z 0.48 1225  94  93  13 0.01
Thu 07/30 13Z 0.48 1224  94  95  13 0.02
Thu 07/30 14Z 0.49 1123  94  96  13 0.02
Thu 07/30 15Z 0.51 1122  95  97  12 0.02
Thu 07/30 16Z 0.52 1020  94  96  12 0.02
Thu 07/30 17Z 0.51 1019  91  96  12 0.01
Thu 07/30 18Z 0.54 0918  88  92  12 0.01
Thu 07/30 19Z 0.56 0917  88  94  12 0.01
Thu 07/30 20Z 0.55 0816  88  95  12 0.02
Thu 07/30 21Z 0.60 0816  91  94  12 0.02
Thu 07/30 22Z 0.57 0816  89  91  12 0.03
Thu 07/30 23Z 0.53 0814  86  90  12 0.01
Fri 07/31 00Z 0.46 0813  86  91  12 0.00
Fri 07/31 01Z 0.38 0711  87  91  12 0.00
Fri 07/31 02Z 0.35 0711  87  89  12 0.00
Fri 07/31 03Z 0.32 0710  87  90  12 0.00
Fri 07/31 04Z 0.29 0710  87  92  12 0.00
Fri 07/31 05Z 0.27 0709  86  89  12 0.00

Run total areal avg QPF for the greens is: 3.29 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