Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260729_0600
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 07/29 06Z 0.04 1615  94  96  13 0.00
Wed 07/29 07Z 0.09 1620  95  94  13 0.00
Wed 07/29 08Z 0.11 1622  94  95  13 0.01
Wed 07/29 09Z 0.19 1523  92  93  13 0.01
Wed 07/29 10Z 0.30 1427  91  91  13 0.01
Wed 07/29 11Z 0.35 1429  88  86  13 0.01
Wed 07/29 12Z 0.29 1428  84  80  13 0.01
Wed 07/29 13Z 0.28 1424  87  72  13 0.01
Wed 07/29 14Z 0.39 1323  84  62  13 0.00
Wed 07/29 15Z 0.59 1323  89  66  13 0.00
Wed 07/29 16Z 0.72 1223  92  70  12 0.01
Wed 07/29 17Z 0.81 1224  95  75  12 0.01
Wed 07/29 18Z 0.72 1223  95  78  12 0.02
Wed 07/29 19Z 0.75 1123  94  79  12 0.02
Wed 07/29 20Z 0.74 1123  92  83  12 0.03
Wed 07/29 21Z 0.64 1123  89  83  12 0.02
Wed 07/29 22Z 0.59 1023  83  84  12 0.01
Wed 07/29 23Z 0.57 1023  81  85  12 0.01
Thu 07/30 00Z 0.58 0922  83  86  12 0.01
Thu 07/30 01Z 0.62 0823  85  89  12 0.01
Thu 07/30 02Z 0.60 0823  82  94  12 0.01
Thu 07/30 03Z 0.58 0822  80  96  12 0.00
Thu 07/30 04Z 0.58 0821  82  96  12 0.00
Thu 07/30 05Z 0.52 0720  84  95  12 0.00
Thu 07/30 06Z 0.52 0619  84  98  12 0.01
Thu 07/30 07Z 0.57 0620  88  97  11 0.04
Thu 07/30 08Z 0.58 0620  91  97  11 0.03
Thu 07/30 09Z 0.53 0519  93  93  11 0.03
Thu 07/30 10Z 0.50 0519  92  89  11 0.03
Thu 07/30 11Z 0.48 0419  91  91  11 0.03
Thu 07/30 12Z 0.46 0420  87  91  11 0.01
Thu 07/30 13Z 0.49 0420  81  93  11 0.01
Thu 07/30 14Z 0.48 0420  76  91  12 0.00
Thu 07/30 15Z 0.55 0320  82  91  11 0.00
Thu 07/30 16Z 1.13 0219  86  87  11 0.00
Thu 07/30 17Z 0.92 0218  89  92  11 0.00
Thu 07/30 18Z 0.88 0219  94  98  11 0.01
Thu 07/30 19Z 0.63 0221  93  98  11 0.02
Thu 07/30 20Z 0.64 0222  92  95  11 0.01
Thu 07/30 21Z 0.56 0321  87  88  11 0.00
Thu 07/30 22Z 0.58 0321  89  81  11 0.00
Thu 07/30 23Z 0.53 0420  89  79  11 0.00
Fri 07/31 00Z 0.48 0420  89  84  11 0.00
Fri 07/31 01Z 0.45 0418  90  81  11 0.00
Fri 07/31 02Z 0.37 0415  90  76  11 0.00
Fri 07/31 03Z 0.30 0313  89  80  11 0.00
Fri 07/31 04Z 0.26 0213  90  82  11 0.00
Fri 07/31 05Z 0.22 0213  89  79  11 0.00
Fri 07/31 06Z 0.19 0113  86  71  11 0.00
Fri 07/31 07Z 0.19 0114  87  66  11 0.00
Fri 07/31 08Z 0.20 0115  90  64  11 0.00
Fri 07/31 09Z 0.22 0115  90  56  11 0.00
Fri 07/31 10Z 0.24 0215  88  51  11 0.00
Fri 07/31 11Z 0.20 0114  87  50  11 0.00
Fri 07/31 12Z 0.16 0113  88  53  11 0.00
Fri 07/31 13Z 0.17 0113  91  56  11 0.00
Fri 07/31 14Z 0.18 0110  93  58  11 0.00
Fri 07/31 15Z 0.15 0109  93  58  11 0.00
Fri 07/31 16Z 0.13 0008  92  57  11 0.00
Fri 07/31 17Z 0.03 3508  91  56  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.45 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