Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260728_1800
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)
=== ===== === ==== ==== === === === ====
Tue 07/28 18Z 0.08 1610  91  78  14 0.00
Tue 07/28 19Z 0.14 1612  90  83  15 0.08
Tue 07/28 20Z 0.10 1713  89  84  15 0.16
Tue 07/28 21Z 0.11 1615  90  86  15 0.13
Tue 07/28 22Z 0.17 1718  93  88  14 0.17
Tue 07/28 23Z 0.13 1721  95  88  14 0.15
Wed 07/29 00Z 0.17 1823  94  86  14 0.13
Wed 07/29 01Z 0.14 1819  92  81  14 0.01
Wed 07/29 02Z 0.07 1621  95  81  14 0.01
Wed 07/29 03Z 0.11 1627  96  82  14 0.02
Wed 07/29 04Z 0.06 1629  97  87  14 0.04
Wed 07/29 05Z 0.04 1728  96  89  14 0.03
Wed 07/29 06Z 0.04 1727  96  92  14 0.03
Wed 07/29 07Z 0.08 1627  95  87  14 0.02
Wed 07/29 08Z 0.13 1628  94  91  14 0.01
Wed 07/29 09Z 0.20 1530  94  91  14 0.02
Wed 07/29 10Z 0.22 1529  96  89  14 0.03
Wed 07/29 11Z 0.33 1430  97  89  14 0.06
Wed 07/29 12Z 0.43 1431  96  91  13 0.09
Wed 07/29 13Z 0.60 1331  97  94  13 0.17
Wed 07/29 14Z 0.75 1336  98  97  13 0.25
Wed 07/29 15Z 0.69 1335  98  97  13 0.19
Wed 07/29 16Z 0.50 1432  99  92  14 0.17
Wed 07/29 17Z 0.40 1430  99  92  14 0.16
Wed 07/29 18Z 0.31 1529  99  95  14 0.20
Wed 07/29 19Z 0.26 1531  98  89  14 0.25
Wed 07/29 20Z 0.32 1426  98  92  14 0.15
Wed 07/29 21Z 0.30 1421  98  95  14 0.12
Wed 07/29 22Z 0.41 1323  97  95  14 0.07
Wed 07/29 23Z 0.49 1224  96  95  14 0.06
Thu 07/30 00Z 0.54 1226  95  94  14 0.15
Thu 07/30 01Z 0.48 1225  96  89  13 0.15
Thu 07/30 02Z 0.45 1226  96  86  14 0.06
Thu 07/30 03Z 0.43 1327  97  92  13 0.07
Thu 07/30 04Z 0.40 1328  97  93  14 0.10
Thu 07/30 05Z 0.39 1327  97  91  13 0.11
Thu 07/30 06Z 0.37 1325  96  85  14 0.04
Thu 07/30 07Z 0.34 1324  96  90  14 0.03
Thu 07/30 08Z 0.34 1324  95  92  14 0.04
Thu 07/30 09Z 0.37 1226  96  92  13 0.11
Thu 07/30 10Z 0.40 1225  95  92  13 0.05
Thu 07/30 11Z 0.46 1226  96  93  13 0.02
Thu 07/30 12Z 0.50 1127  96  93  13 0.02
Thu 07/30 13Z 0.49 1126  96  94  13 0.02
Thu 07/30 14Z 0.49 1124  97  95  13 0.02
Thu 07/30 15Z 0.51 1124  97  96  12 0.03
Thu 07/30 16Z 0.54 1023  97  95  12 0.02
Thu 07/30 17Z 0.54 1022  94  96  12 0.02
Thu 07/30 18Z 0.60 0920  91  90  12 0.01
Thu 07/30 19Z 0.61 0819  92  92  12 0.02
Thu 07/30 20Z 0.60 0818  92  94  12 0.03
Thu 07/30 21Z 0.66 0718  94  95  11 0.04
Thu 07/30 22Z 0.61 0817  91  95  11 0.04
Thu 07/30 23Z 0.58 0716  90  94  11 0.01
Fri 07/31 00Z 0.53 0715  91  96  12 0.01
Fri 07/31 01Z 0.44 0713  91  94  12 0.00
Fri 07/31 02Z 0.41 0712  91  91  12 0.00
Fri 07/31 03Z 0.38 0712  91  91  12 0.00
Fri 07/31 04Z 0.33 0611  92  91  12 0.00
Fri 07/31 05Z 0.30 0610  92  87  12 0.00

Run total areal avg QPF for the Central_Greens is: 4.20 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